diff --git a/fetch.sh b/fetch.sh
index 710eaaf..dda8c13 100755
--- a/fetch.sh
+++ b/fetch.sh
@@ -8,13 +8,9 @@ fi
 list=$(find -name "Day*.cpp" | awk -F '/' '{print $3 "/" $4}' | awk -F '.' '{print $1}' | sed 's/Day//g' | sort)
 
 for item in $list; do
-    echo $item
     year=$(echo $item | awk -F '/' '{print $1}')
     day=$(echo $item | awk -F '/' '{print $2}')
-    echo "year: $year"
-    echo "day: $day"
     dir="res/$year/day$day/input.txt"
-    echo $dir
     if [ ! -e $dir ]; then
         webitem=$(echo $day | sed 's/^0//g')
         echo "Fetching $dir"
diff --git a/res/2021/day01/test_input.txt b/res/2021/day01/test_input.txt
new file mode 100644
index 0000000..59dad67
--- /dev/null
+++ b/res/2021/day01/test_input.txt
@@ -0,0 +1,10 @@
+199
+200
+208
+210
+200
+207
+240
+269
+260
+263
\ No newline at end of file
diff --git a/res/2021/day02/test_input.txt b/res/2021/day02/test_input.txt
new file mode 100644
index 0000000..0ed302d
--- /dev/null
+++ b/res/2021/day02/test_input.txt
@@ -0,0 +1,6 @@
+forward 5
+down 5
+forward 8
+up 3
+down 8
+forward 2
\ No newline at end of file
diff --git a/res/2021/day03/test_input.txt b/res/2021/day03/test_input.txt
new file mode 100644
index 0000000..665fd57
--- /dev/null
+++ b/res/2021/day03/test_input.txt
@@ -0,0 +1,12 @@
+00100
+11110
+10110
+10111
+10101
+01111
+00111
+11100
+10000
+11001
+00010
+01010
\ No newline at end of file
diff --git a/res/2021/day04/test_input.txt b/res/2021/day04/test_input.txt
new file mode 100644
index 0000000..49d17bc
--- /dev/null
+++ b/res/2021/day04/test_input.txt
@@ -0,0 +1,19 @@
+7,4,9,5,11,17,23,2,0,14,21,24,10,16,13,6,15,25,12,22,18,20,8,19,3,26,1
+
+22 13 17 11  0
+ 8  2 23  4 24
+21  9 14 16  7
+ 6 10  3 18  5
+ 1 12 20 15 19
+
+ 3 15  0  2 22
+ 9 18 13 17  5
+19  8  7 25 23
+20 11 10 24  4
+14 21 16 12  6
+
+14 21 17 24  4
+10 16 15  9 19
+18  8 23 26 20
+22 11 13  6  5
+ 2  0 12  3  7
\ No newline at end of file
diff --git a/res/2021/day05/test_input.txt b/res/2021/day05/test_input.txt
new file mode 100644
index 0000000..1d4e36d
--- /dev/null
+++ b/res/2021/day05/test_input.txt
@@ -0,0 +1,10 @@
+0,9 -> 5,9
+8,0 -> 0,8
+9,4 -> 3,4
+2,2 -> 2,1
+7,0 -> 7,4
+6,4 -> 2,0
+0,9 -> 2,9
+3,4 -> 1,4
+0,0 -> 8,8
+5,5 -> 8,2
\ No newline at end of file
diff --git a/res/2021/day06/test_input.txt b/res/2021/day06/test_input.txt
new file mode 100644
index 0000000..a7af2b1
--- /dev/null
+++ b/res/2021/day06/test_input.txt
@@ -0,0 +1 @@
+3,4,3,1,2
\ No newline at end of file
diff --git a/res/2021/day07/test_input.txt b/res/2021/day07/test_input.txt
new file mode 100644
index 0000000..2bdd92f
--- /dev/null
+++ b/res/2021/day07/test_input.txt
@@ -0,0 +1 @@
+16,1,2,0,4,2,7,1,2,14
\ No newline at end of file
diff --git a/res/2021/day08/test_input.txt b/res/2021/day08/test_input.txt
new file mode 100644
index 0000000..8614893
--- /dev/null
+++ b/res/2021/day08/test_input.txt
@@ -0,0 +1,10 @@
+be cfbegad cbdgef fgaecd cgeb fdcge agebfd fecdb fabcd edb | fdgacbe cefdb cefbgd gcbe
+edbfga begcd cbg gc gcadebf fbgde acbgfd abcde gfcbed gfec | fcgedb cgb dgebacf gc
+fgaebd cg bdaec gdafb agbcfd gdcbef bgcad gfac gcb cdgabef | cg cg fdcagb cbg
+fbegcd cbd adcefb dageb afcb bc aefdc ecdab fgdeca fcdbega | efabcd cedba gadfec cb
+aecbfdg fbg gf bafeg dbefa fcge gcbea fcaegb dgceab fcbdga | gecf egdcabf bgf bfgea
+fgeab ca afcebg bdacfeg cfaedg gcfdb baec bfadeg bafgc acf | gebdcfa ecba ca fadegcb
+dbcfg fgd bdegcaf fgec aegbdf ecdfab fbedc dacgb gdcebf gf | cefg dcbef fcge gbcadfe
+bdfegc cbegaf gecbf dfcage bdacg ed bedf ced adcbefg gebcd | ed bcgafe cdgba cbgef
+egadfb cdbfeg cegd fecab cgb gbdefca cg fgcdab egfdb bfceg | gbdfcae bgc cg cgb
+gcafb gcf dcaebfg ecagb gf abcdeg gaef cafbge fdbac fegbdc | fgae cfgab fg bagce
\ No newline at end of file
diff --git a/res/2021/day09/test_input.txt b/res/2021/day09/test_input.txt
new file mode 100644
index 0000000..610bad9
--- /dev/null
+++ b/res/2021/day09/test_input.txt
@@ -0,0 +1,5 @@
+2199943210
+3987894921
+9856789892
+8767896789
+9899965678
\ No newline at end of file
diff --git a/res/2021/day10/test_input.txt b/res/2021/day10/test_input.txt
new file mode 100644
index 0000000..2f182d8
--- /dev/null
+++ b/res/2021/day10/test_input.txt
@@ -0,0 +1,10 @@
+[({(<(())[]>[[{[]{<()<>>
+[(()[<>])]({[<{<<[]>>(
+{([(<{}[<>[]}>{[]{[(<()>
+(((({<>}<{<{<>}{[]{[]{}
+[[<[([]))<([[{}[[()]]]
+[{[{({}]{}}([{[{{{}}([]
+{<[[]]>}<{[{[{[]{()[[[]
+[<(<(<(<{}))><([]([]()
+<{([([[(<>()){}]>(<<{{
+<{([{{}}[<[[[<>{}]]]>[]]
\ No newline at end of file
diff --git a/res/2021/day11/test_input.txt b/res/2021/day11/test_input.txt
new file mode 100644
index 0000000..a3819c9
--- /dev/null
+++ b/res/2021/day11/test_input.txt
@@ -0,0 +1,10 @@
+5483143223
+2745854711
+5264556173
+6141336146
+6357385478
+4167524645
+2176841721
+6882881134
+4846848554
+5283751526
\ No newline at end of file
diff --git a/res/2021/day12/test_input.txt b/res/2021/day12/test_input.txt
new file mode 100644
index 0000000..6fd8c41
--- /dev/null
+++ b/res/2021/day12/test_input.txt
@@ -0,0 +1,7 @@
+start-A
+start-b
+A-c
+A-b
+b-d
+A-end
+b-end
diff --git a/res/2021/day13/test_input.txt b/res/2021/day13/test_input.txt
new file mode 100644
index 0000000..32a8563
--- /dev/null
+++ b/res/2021/day13/test_input.txt
@@ -0,0 +1,21 @@
+6,10
+0,14
+9,10
+0,3
+10,4
+4,11
+6,0
+6,12
+4,1
+0,13
+10,12
+3,4
+3,0
+8,4
+1,10
+2,14
+8,10
+9,0
+
+fold along y=7
+fold along x=5
\ No newline at end of file
diff --git a/res/2021/day14/test_input.txt b/res/2021/day14/test_input.txt
new file mode 100644
index 0000000..6c1c3a1
--- /dev/null
+++ b/res/2021/day14/test_input.txt
@@ -0,0 +1,18 @@
+NNCB
+
+CH -> B
+HH -> N
+CB -> H
+NH -> C
+HB -> C
+HC -> B
+HN -> C
+NN -> C
+BH -> H
+NC -> B
+NB -> B
+BN -> B
+BB -> N
+BC -> B
+CC -> N
+CN -> C
\ No newline at end of file
diff --git a/res/2021/day15/test_input.txt b/res/2021/day15/test_input.txt
new file mode 100644
index 0000000..7d9d562
--- /dev/null
+++ b/res/2021/day15/test_input.txt
@@ -0,0 +1,10 @@
+1163751742
+1381373672
+2136511328
+3694931569
+7463417111
+1319128137
+1359912421
+3125421639
+1293138521
+2311944581
\ No newline at end of file
diff --git a/res/2021/day16/test_input.txt b/res/2021/day16/test_input.txt
new file mode 100644
index 0000000..4ced67a
--- /dev/null
+++ b/res/2021/day16/test_input.txt
@@ -0,0 +1 @@
+9C0141080250320F1802104A08
diff --git a/res/2021/day17/test_input.txt b/res/2021/day17/test_input.txt
new file mode 100644
index 0000000..f40609b
--- /dev/null
+++ b/res/2021/day17/test_input.txt
@@ -0,0 +1 @@
+target area: x=20..30, y=-10..-5
\ No newline at end of file
diff --git a/res/2021/day18/test_input.txt b/res/2021/day18/test_input.txt
new file mode 100644
index 0000000..1368dc4
--- /dev/null
+++ b/res/2021/day18/test_input.txt
@@ -0,0 +1,10 @@
+[[[0,[5,8]],[[1,7],[9,6]]],[[4,[1,2]],[[1,4],2]]]
+[[[5,[2,8]],4],[5,[[9,9],0]]]
+[6,[[[6,2],[5,6]],[[7,6],[4,7]]]]
+[[[6,[0,7]],[0,9]],[4,[9,[9,0]]]]
+[[[7,[6,4]],[3,[1,3]]],[[[5,5],1],9]]
+[[6,[[7,3],[3,2]]],[[[3,8],[5,7]],4]]
+[[[[5,4],[7,7]],8],[[8,3],8]]
+[[9,3],[[9,9],[6,[4,9]]]]
+[[2,[[7,7],7]],[[5,8],[[9,3],[0,2]]]]
+[[[[5,2],5],[8,[3,7]]],[[5,[7,5]],[4,4]]]
diff --git a/res/2021/day19/test_input.txt b/res/2021/day19/test_input.txt
new file mode 100644
index 0000000..b596cc4
--- /dev/null
+++ b/res/2021/day19/test_input.txt
@@ -0,0 +1,136 @@
+--- scanner 0 ---
+404,-588,-901
+528,-643,409
+-838,591,734
+390,-675,-793
+-537,-823,-458
+-485,-357,347
+-345,-311,381
+-661,-816,-575
+-876,649,763
+-618,-824,-621
+553,345,-567
+474,580,667
+-447,-329,318
+-584,868,-557
+544,-627,-890
+564,392,-477
+455,729,728
+-892,524,684
+-689,845,-530
+423,-701,434
+7,-33,-71
+630,319,-379
+443,580,662
+-789,900,-551
+459,-707,401
+
+--- scanner 1 ---
+686,422,578
+605,423,415
+515,917,-361
+-336,658,858
+95,138,22
+-476,619,847
+-340,-569,-846
+567,-361,727
+-460,603,-452
+669,-402,600
+729,430,532
+-500,-761,534
+-322,571,750
+-466,-666,-811
+-429,-592,574
+-355,545,-477
+703,-491,-529
+-328,-685,520
+413,935,-424
+-391,539,-444
+586,-435,557
+-364,-763,-893
+807,-499,-711
+755,-354,-619
+553,889,-390
+
+--- scanner 2 ---
+649,640,665
+682,-795,504
+-784,533,-524
+-644,584,-595
+-588,-843,648
+-30,6,44
+-674,560,763
+500,723,-460
+609,671,-379
+-555,-800,653
+-675,-892,-343
+697,-426,-610
+578,704,681
+493,664,-388
+-671,-858,530
+-667,343,800
+571,-461,-707
+-138,-166,112
+-889,563,-600
+646,-828,498
+640,759,510
+-630,509,768
+-681,-892,-333
+673,-379,-804
+-742,-814,-386
+577,-820,562
+
+--- scanner 3 ---
+-589,542,597
+605,-692,669
+-500,565,-823
+-660,373,557
+-458,-679,-417
+-488,449,543
+-626,468,-788
+338,-750,-386
+528,-832,-391
+562,-778,733
+-938,-730,414
+543,643,-506
+-524,371,-870
+407,773,750
+-104,29,83
+378,-903,-323
+-778,-728,485
+426,699,580
+-438,-605,-362
+-469,-447,-387
+509,732,623
+647,635,-688
+-868,-804,481
+614,-800,639
+595,780,-596
+
+--- scanner 4 ---
+727,592,562
+-293,-554,779
+441,611,-461
+-714,465,-776
+-743,427,-804
+-660,-479,-426
+832,-632,460
+927,-485,-438
+408,393,-506
+466,436,-512
+110,16,151
+-258,-428,682
+-393,719,612
+-211,-452,876
+808,-476,-593
+-575,615,604
+-485,667,467
+-680,325,-822
+-627,-443,-432
+872,-547,-609
+833,512,582
+807,604,487
+839,-516,451
+891,-625,532
+-652,-548,-490
+30,-46,-14
\ No newline at end of file
diff --git a/res/2021/day20/test_input.txt b/res/2021/day20/test_input.txt
new file mode 100644
index 0000000..000a554
--- /dev/null
+++ b/res/2021/day20/test_input.txt
@@ -0,0 +1,7 @@
+..#.#..#####.#.#.#.###.##.....###.##.#..###.####..#####..#....#..#..##..###..######.###...####..#..#####..##..#.#####...##.#.#..#.##..#.#......#.###.######.###.####...#.##.##..#..#..#####.....#.#....###..#.##......#.....#..#..#..##..#...##.######.####.####.#.#...#.......#..#.#.#...####.##.#......#..#...##.#.##..#...##.#.##..###.#......#.#.......#.#.#.####.###.##...#.....####.#..#..#.##.#....##..#.####....##...##..#...#......#.#.......#.......##..####..#...#.#.#...##..#.#..###..#####........#..####......#..#
+
+#..#.
+#....
+##..#
+..#..
+..###
\ No newline at end of file
diff --git a/res/2021/day21/test_input.txt b/res/2021/day21/test_input.txt
new file mode 100644
index 0000000..6dec3f4
--- /dev/null
+++ b/res/2021/day21/test_input.txt
@@ -0,0 +1,2 @@
+Player 1 starting position: 4
+Player 2 starting position: 8
\ No newline at end of file
diff --git a/res/2021/day22/test_input.txt b/res/2021/day22/test_input.txt
new file mode 100644
index 0000000..2790bed
--- /dev/null
+++ b/res/2021/day22/test_input.txt
@@ -0,0 +1,60 @@
+on x=-5..47,y=-31..22,z=-19..33
+on x=-44..5,y=-27..21,z=-14..35
+on x=-49..-1,y=-11..42,z=-10..38
+on x=-20..34,y=-40..6,z=-44..1
+off x=26..39,y=40..50,z=-2..11
+on x=-41..5,y=-41..6,z=-36..8
+off x=-43..-33,y=-45..-28,z=7..25
+on x=-33..15,y=-32..19,z=-34..11
+off x=35..47,y=-46..-34,z=-11..5
+on x=-14..36,y=-6..44,z=-16..29
+on x=-57795..-6158,y=29564..72030,z=20435..90618
+on x=36731..105352,y=-21140..28532,z=16094..90401
+on x=30999..107136,y=-53464..15513,z=8553..71215
+on x=13528..83982,y=-99403..-27377,z=-24141..23996
+on x=-72682..-12347,y=18159..111354,z=7391..80950
+on x=-1060..80757,y=-65301..-20884,z=-103788..-16709
+on x=-83015..-9461,y=-72160..-8347,z=-81239..-26856
+on x=-52752..22273,y=-49450..9096,z=54442..119054
+on x=-29982..40483,y=-108474..-28371,z=-24328..38471
+on x=-4958..62750,y=40422..118853,z=-7672..65583
+on x=55694..108686,y=-43367..46958,z=-26781..48729
+on x=-98497..-18186,y=-63569..3412,z=1232..88485
+on x=-726..56291,y=-62629..13224,z=18033..85226
+on x=-110886..-34664,y=-81338..-8658,z=8914..63723
+on x=-55829..24974,y=-16897..54165,z=-121762..-28058
+on x=-65152..-11147,y=22489..91432,z=-58782..1780
+on x=-120100..-32970,y=-46592..27473,z=-11695..61039
+on x=-18631..37533,y=-124565..-50804,z=-35667..28308
+on x=-57817..18248,y=49321..117703,z=5745..55881
+on x=14781..98692,y=-1341..70827,z=15753..70151
+on x=-34419..55919,y=-19626..40991,z=39015..114138
+on x=-60785..11593,y=-56135..2999,z=-95368..-26915
+on x=-32178..58085,y=17647..101866,z=-91405..-8878
+on x=-53655..12091,y=50097..105568,z=-75335..-4862
+on x=-111166..-40997,y=-71714..2688,z=5609..50954
+on x=-16602..70118,y=-98693..-44401,z=5197..76897
+on x=16383..101554,y=4615..83635,z=-44907..18747
+off x=-95822..-15171,y=-19987..48940,z=10804..104439
+on x=-89813..-14614,y=16069..88491,z=-3297..45228
+on x=41075..99376,y=-20427..49978,z=-52012..13762
+on x=-21330..50085,y=-17944..62733,z=-112280..-30197
+on x=-16478..35915,y=36008..118594,z=-7885..47086
+off x=-98156..-27851,y=-49952..43171,z=-99005..-8456
+off x=2032..69770,y=-71013..4824,z=7471..94418
+on x=43670..120875,y=-42068..12382,z=-24787..38892
+off x=37514..111226,y=-45862..25743,z=-16714..54663
+off x=25699..97951,y=-30668..59918,z=-15349..69697
+off x=-44271..17935,y=-9516..60759,z=49131..112598
+on x=-61695..-5813,y=40978..94975,z=8655..80240
+off x=-101086..-9439,y=-7088..67543,z=33935..83858
+off x=18020..114017,y=-48931..32606,z=21474..89843
+off x=-77139..10506,y=-89994..-18797,z=-80..59318
+off x=8476..79288,y=-75520..11602,z=-96624..-24783
+on x=-47488..-1262,y=24338..100707,z=16292..72967
+off x=-84341..13987,y=2429..92914,z=-90671..-1318
+off x=-37810..49457,y=-71013..-7894,z=-105357..-13188
+off x=-27365..46395,y=31009..98017,z=15428..76570
+off x=-70369..-16548,y=22648..78696,z=-1892..86821
+on x=-53470..21291,y=-120233..-33476,z=-44150..38147
+off x=-93533..-4276,y=-16170..68771,z=-104985..-24507
\ No newline at end of file
diff --git a/res/2021/day23/test_input.txt b/res/2021/day23/test_input.txt
new file mode 100644
index 0000000..56a84a1
--- /dev/null
+++ b/res/2021/day23/test_input.txt
@@ -0,0 +1,5 @@
+#############
+#...........#
+###B#C#B#D###
+  #A#D#C#A#
+  #########
\ No newline at end of file
diff --git a/res/2021/day24/test_input.txt b/res/2021/day24/test_input.txt
new file mode 100644
index 0000000..e69de29
diff --git a/res/2021/day25/test_input.txt b/res/2021/day25/test_input.txt
new file mode 100644
index 0000000..0f3c0cd
--- /dev/null
+++ b/res/2021/day25/test_input.txt
@@ -0,0 +1,9 @@
+v...>>.vv>
+.vv>>.vv..
+>>.>v>...v
+>>v>>.>.v.
+v>v.vv.v..
+>.>>..v...
+.vv..>.>v.
+v.v..>>v.v
+....v..v.>
diff --git a/src/2021/Day01.cpp b/src/2021/Day01.cpp
new file mode 100644
index 0000000..711dae4
--- /dev/null
+++ b/src/2021/Day01.cpp
@@ -0,0 +1,38 @@
+#include "common/aoc.h"
+
+namespace y2021::day01
+{
+  REGISTER_DAY(2021, Day01, std::vector<int>, int);
+
+  REGISTER_TEST_EXAMPLE(2021, Day01, ExampleInput, 1, 7);
+  REGISTER_TEST(2021, Day01, Input, 1, 1722);
+  REGISTER_TEST_EXAMPLE(2021, Day01, ExampleInput, 2, 5);
+  REGISTER_TEST(2021, Day01, Input, 2, 1748);
+
+  READ_INPUT(input)
+  {
+    return Input::ReadInts(input);
+  }
+
+  OUTPUT1(input)
+  {
+    int count = 0;
+    for (size_t i = 0; i < input.size() - 1; i++)
+    {
+      if (input[i] < input[i + 1])
+        count++;
+    }
+    return count;
+  }
+
+  OUTPUT2(input)
+  {
+    int count = 0;
+    for (size_t i = 0; i < input.size() - 3; i++)
+    {
+      if (input[i] + input[i + 1] + input[i + 2] < input[i + 1] + input[i + 2] + input[i + 3])
+        count++;
+    }
+    return count;
+  }
+}
diff --git a/src/2021/Day02.cpp b/src/2021/Day02.cpp
new file mode 100644
index 0000000..d2842e9
--- /dev/null
+++ b/src/2021/Day02.cpp
@@ -0,0 +1,90 @@
+#include "common/aoc.h"
+
+namespace y2021::day02
+{
+  enum class Dir
+  {
+    Forward,
+    Down,
+    Up
+  };
+
+  struct Move
+  {
+    Dir dir;
+    int amount;
+  };
+
+  REGISTER_DAY(2021, Day02, std::vector<Move>, int);
+
+  REGISTER_TEST_EXAMPLE(2021, Day02, ExampleInput, 1, 150);
+  REGISTER_TEST(2021, Day02, Input, 1, 1815044);
+  REGISTER_TEST_EXAMPLE(2021, Day02, ExampleInput, 2, 900);
+  REGISTER_TEST(2021, Day02, Input, 2, 1739283308);
+
+  READ_INPUT(input)
+  {
+    std::vector<Move> moves;
+    std::string str;
+    while (getline(input, str))
+    {
+      std::stringstream ss{str};
+      std::string s;
+      int i;
+      ss >> s >> i;
+      if (s == "forward")
+        moves.emplace_back(Move{Dir::Forward, i});
+      else if (s == "down")
+        moves.emplace_back(Move{Dir::Down, i});
+      else if (s == "up")
+        moves.emplace_back(Move{Dir::Up, i});
+    }
+    return moves;
+  }
+
+  OUTPUT1(input)
+  {
+    int x = 0;
+    int y = 0;
+    for (auto&& move : input)
+    {
+      switch (move.dir)
+      {
+        case Dir::Forward:
+          x += move.amount;
+          break;
+        case Dir::Down:
+          y += move.amount;
+          break;
+        case Dir::Up:
+          y -= move.amount;
+          break;
+      }
+    }
+    return x * y;
+  }
+
+  OUTPUT2(input)
+  {
+    int x = 0;
+    int y = 0;
+    int aim = 0;
+    for (auto&& move : input)
+    {
+      switch (move.dir)
+      {
+        case Dir::Forward:
+          x += move.amount;
+          y += aim * move.amount;
+          break;
+        case Dir::Down:
+          aim += move.amount;
+          break;
+        case Dir::Up:
+          aim -= move.amount;
+          break;
+      }
+    }
+    return x * y;
+  }
+}
diff --git a/src/2021/Day03.cpp b/src/2021/Day03.cpp
new file mode 100644
index 0000000..f025a5b
--- /dev/null
+++ b/src/2021/Day03.cpp
@@ -0,0 +1,94 @@
+#include "common/aoc.h"
+
+namespace y2021::day03
+{
+  REGISTER_DAY(2021, Day03, std::set<std::string>, int);
+
+  REGISTER_TEST_EXAMPLE(2021, Day03, ExampleInput, 1, 198);
+  REGISTER_TEST(2021, Day03, Input, 1, 2498354);
+  REGISTER_TEST_EXAMPLE(2021, Day03, ExampleInput, 2, 230);
+  REGISTER_TEST(2021, Day03, Input, 2, 3277956);
+
+  READ_INPUT(input)
+  {
+    std::set<std::string> strings;
+    std::string str;
+    while (getline(input, str))
+    {
+      strings.emplace(str);
+    }
+    return strings;
+  }
+
+  OUTPUT1(input)
+  {
+    int gamma = 0;
+    int width = input.begin()->size();
+    for (int x = 0; x < width; x++)
+    {
+      size_t count = 0;
+      for (auto&& str : input)
+      {
+        if (str[x] == '1')
+          count++;
+      }
+      if (count >= input.size() / 2)
+      {
+        gamma |= BIT(width - x - 1);
+      }
+    }
+    int invertMask = BIT(width) - 1;
+    return gamma * (gamma ^ invertMask);
+  }
+
+  OUTPUT2(input)
+  {
+    int width = input.begin()->size();
+
+    std::set<std::string> oxygen = input;
+    std::set<std::string> carbon = input;
+    for (int i = 0; i < width; i++)
+    {
+      char mostCommon = '0';
+      size_t count = 0;
+      for (auto it = oxygen.begin(); it != oxygen.end(); it++)
+      {
+        if (it->at(i) == '1')
+          count++;
+      }
+      if (count * 2 >= oxygen.size())
+        mostCommon = '1';
+      for (auto it = oxygen.begin(); it != oxygen.end();)
+      {
+        if (oxygen.size() == 1)
+          break;
+        if (it->at(i) != mostCommon)
+          it = oxygen.erase(it);
+        else
+          it++;
+      }
+
+      char leastCommon = '0';
+      count = 0;
+      for (auto it = carbon.begin(); it != carbon.end(); it++)
+      {
+        if (it->at(i) == '1')
+          count++;
+      }
+      if (count * 2 < carbon.size())
+        leastCommon = '1';
+      for (auto it = carbon.begin(); it != carbon.end();)
+      {
+        if (carbon.size() == 1)
+          break;
+        if (it->at(i) != leastCommon)
+          it = carbon.erase(it);
+        else
+          it++;
+      }
+    }
+    int oxygenVal = Helper::BinStrToInt(*oxygen.begin());
+    int carbonVal = Helper::BinStrToInt(*carbon.begin());
+    return oxygenVal * carbonVal;
+  }
+}
diff --git a/src/2021/Day04.cpp b/src/2021/Day04.cpp
new file mode 100644
index 0000000..2d7818b
--- /dev/null
+++ b/src/2021/Day04.cpp
@@ -0,0 +1,127 @@
+#include "common/aoc.h"
+
+namespace y2021::day04
+{
+  struct Game
+  {
+    std::vector<int> input;
+    std::vector<Array2D<int>> boards;
+  };
+
+  bool MarkAndCheck(Array2D<int>& board, int number)
+  {
+    Index2D index = board.Find(number);
+    if (index)
+    {
+      board[index] = -1;
+      // Check board is filled
+      bool filledX = true;
+      bool filledY = true;
+      for (int i = 0; i < 5; i++)
+      {
+        if (board.Get(i, index.y) != -1)
+          filledX = false;
+        if (board.Get(index.x, i) != -1)
+          filledY = false;
+      }
+      return filledX || filledY;
+    }
+    return false;
+  }
+
+  REGISTER_DAY(2021, Day04, Game, int);
+
+  REGISTER_TEST_EXAMPLE(2021, Day04, ExampleInput, 1, 4512);
+  REGISTER_TEST(2021, Day04, Input, 1, 54275);
+  REGISTER_TEST_EXAMPLE(2021, Day04, ExampleInput, 2, 1924);
+  REGISTER_TEST(2021, Day04, Input, 2, 13158);
+
+  READ_INPUT(input)
+  {
+    Game game;
+    std::string str;
+    getline(input, str);
+    std::stringstream ss{str};
+    while (getline(ss, str, ','))
+    {
+      game.input.emplace_back(atoi(str.c_str()));
+    }
+    getline(input, str);
+    while (!input.eof())
+    {
+      Array2D<int> array2D{5, 5};
+      for (int y = 0; y < 5; y++)
+      {
+        getline(input, str);
+        std::stringstream ss{str};
+        for (int x = 0; x < 5; x++)
+        {
+          int i;
+          ss >> i;
+          array2D.Set(x, y, i);
+        }
+      }
+      game.boards.emplace_back(array2D);
+      getline(input, str);
+    }
+    return game;
+  }
+
+  OUTPUT1(input)
+  {
+    Game game = input;  // Copy the data to be able to modify it
+    int winner = -1;
+    int i = 0;
+    while (winner == -1)
+    {
+      int number = game.input[i];
+      for (auto& board : game.boards)
+      {
+        if (MarkAndCheck(board, number))
+        {
+          int total = 0;
+          for (auto& val : board)
+          {
+            if (val != -1)
+              total += val;
+          }
+          return total * number;
+        }
+      }
+      i++;
+    }
+    return 0;
+  }
+
+  OUTPUT2(input)
+  {
+    Game game = input;  // Copy the data to be able to modify it
+    int winner = -1;
+    int i = 0;
+    while (winner == -1)
+    {
+      int number = game.input[i];
+      for (auto it = game.boards.begin(); it != game.boards.end();)
+      {
+        if (MarkAndCheck(*it, number))
+        {
+          if (game.boards.size() == 1)
+          {
+            int total = 0;
+            for (auto& val : game.boards.front())
+            {
+              if (val != -1)
+                total += val;
+            }
+            return total * number;
+          }
+          it = game.boards.erase(it);
+        }
+        else
+          it++;
+      }
+      i++;
+    }
+    return 0;
+  }
+}
diff --git a/src/2021/Day05.cpp b/src/2021/Day05.cpp
new file mode 100644
index 0000000..625dbbb
--- /dev/null
+++ b/src/2021/Day05.cpp
@@ -0,0 +1,96 @@
+#include "common/aoc.h"
+
+namespace y2021::day05
+{
+  struct Line
+  {
+    int x1;
+    int y1;
+    int x2;
+    int y2;
+  };
+
+  REGISTER_DAY(2021, Day05, std::vector<Line>, int);
+
+  REGISTER_TEST_EXAMPLE(2021, Day05, ExampleInput, 1, 5);
+  REGISTER_TEST(2021, Day05, Input, 1, 5442);
+  REGISTER_TEST_EXAMPLE(2021, Day05, ExampleInput, 2, 12);
+  REGISTER_TEST(2021, Day05, Input, 2, 19571);
+
+  READ_INPUT(input)
+  {
+    std::string str;
+    std::vector<Line> lines;
+    while (getline(input, str))
+    {
+      std::stringstream ss{str};
+      Line line;
+      ss >> line.x1 >> "," >> line.y1 >> "->" >> line.x2 >> "," >> line.y2;
+      lines.emplace_back(line);
+    }
+    return lines;
+  }
+
+  OUTPUT1(input)
+  {
+    Index2D max;
+    for (auto& line : input)
+    {
+      max.x = std::max({max.x, line.x1, line.x2});
+      max.y = std::max({max.y, line.y1, line.y2});
+    }
+    Array2D<uint8_t> overlap{max.x + 1, max.y + 1};
+    for (auto& line : input)
+    {
+      if (line.x1 == line.x2 || line.y1 == line.y2)
+      {
+        int width = std::max(std::abs(line.x1 - line.x2), std::abs(line.y1 - line.y2)) + 1;
+        int deltaX = Helper::Sign(line.x2 - line.x1);
+        int deltaY = Helper::Sign(line.y2 - line.y1);
+        for (int i = 0; i < width; i++)
+        {
+          Index2D index{line.x1 + deltaX * i, line.y1 + deltaY * i};
+          overlap[index]++;
+        }
+      }
+    }
+    int count = 0;
+    overlap.Each(
+      [&](const Array2D<uint8_t>& overlap, const Index2D& index)
+      {
+        if (overlap[index] > 1)
+          count++;
+      });
+    return count;
+  }
+
+  OUTPUT2(input)
+  {
+    Index2D max;
+    for (auto& line : input)
+    {
+      max.x = std::max({max.x, line.x1, line.x2});
+      max.y = std::max({max.y, line.y1, line.y2});
+    }
+    Array2D<uint8_t> overlap{max.x + 1, max.y + 1};
+    for (auto& line : input)
+    {
+      int width = std::max(std::abs(line.x1 - line.x2), std::abs(line.y1 - line.y2)) + 1;
+      int deltaX = Helper::Sign(line.x2 - line.x1);
+      int deltaY = Helper::Sign(line.y2 - line.y1);
+      for (int i = 0; i < width; i++)
+      {
+        Index2D index{line.x1 + deltaX * i, line.y1 + deltaY * i};
+        overlap[index]++;
+      }
+    }
+    int count = 0;
+    overlap.Each(
+      [&](const Array2D<uint8_t>& overlap, const Index2D& index)
+      {
+        if (overlap[index] > 1)
+          count++;
+      });
+    return count;
+  }
+}
diff --git a/src/2021/Day06.cpp b/src/2021/Day06.cpp
new file mode 100644
index 0000000..26b243c
--- /dev/null
+++ b/src/2021/Day06.cpp
@@ -0,0 +1,52 @@
+#include "common/aoc.h"
+
+namespace y2021::day06
+{
+
+  int64_t GetPopulation(std::vector<int64_t>& lenternfishes, int days)
+  {
+    for (int i = 0; i < days; i++)
+    {
+      int64_t newBorn = lenternfishes[0];
+      for (size_t j = 1; j < lenternfishes.size(); j++)
+      {
+        lenternfishes[j - 1] = lenternfishes[j];
+      }
+      lenternfishes[8] = newBorn;
+      lenternfishes[6] += newBorn;
+    }
+    return Helper::Sum<int64_t>(lenternfishes);
+  }
+
+  REGISTER_DAY(2021, Day06, std::vector<int64_t>, int64_t);
+
+  REGISTER_TEST_EXAMPLE(2021, Day06, ExampleInput, 1, 5934);
+  REGISTER_TEST(2021, Day06, Input, 1, 374994);
+  REGISTER_TEST_EXAMPLE(2021, Day06, ExampleInput, 2, 26984457539);
+  REGISTER_TEST(2021, Day06, Input, 2, 1686252324092);
+
+  READ_INPUT(input)
+  {
+    std::vector<int64_t> ints;
+    ints.resize(9);
+
+    std::string str;
+    while (getline(input, str, ','))
+    {
+      ints[atoi(str.c_str())]++;
+    }
+    return ints;
+  }
+
+  OUTPUT1(inputConst)
+  {
+    InputType input = inputConst;
+    return GetPopulation(input, 80);
+  }
+
+  OUTPUT2(inputConst)
+  {
+    InputType input = inputConst;
+    return GetPopulation(input, 256);
+  }
+}
diff --git a/src/2021/Day07.cpp b/src/2021/Day07.cpp
new file mode 100644
index 0000000..c8b0207
--- /dev/null
+++ b/src/2021/Day07.cpp
@@ -0,0 +1,51 @@
+#include "common/aoc.h"
+
+namespace y2021::day07
+{
+  REGISTER_DAY(2021, Day07, std::vector<int>, int);
+
+  REGISTER_TEST_EXAMPLE(2021, Day07, ExampleInput, 1, 37);
+  REGISTER_TEST(2021, Day07, Input, 1, 359648);
+  REGISTER_TEST_EXAMPLE(2021, Day07, ExampleInput, 2, 168);
+  REGISTER_TEST(2021, Day07, Input, 2, 100727924);
+
+  READ_INPUT(input)
+  {
+    return Input::ReadInts(input, ',');
+  }
+
+  OUTPUT1(input)
+  {
+    int max = Helper::Max(input);
+    int min = Helper::Min(input);
+    int minCost = std::numeric_limits<int>::max();
+    for (int i = min; i < max + 1; i++)
+    {
+      int cost = 0;
+      for (auto num : input)
+      {
+        cost += std::abs(num - i);
+      }
+      minCost = std::min(minCost, cost);
+    }
+    return minCost;
+  }
+
+  OUTPUT2(input)
+  {
+    int max = Helper::Max(input);
+    int min = Helper::Min(input);
+    int minCost = std::numeric_limits<int>::max();
+    for (int i = min; i < max + 1; i++)
+    {
+      int cost = 0;
+      for (auto num : input)
+      {
+        int steps = std::abs(num - i);
+        cost += steps * (steps + 1) / 2;
+      }
+      minCost = std::min(minCost, cost);
+    }
+    return minCost;
+  }
+}
diff --git a/src/2021/Day08.cpp b/src/2021/Day08.cpp
new file mode 100644
index 0000000..3483ddc
--- /dev/null
+++ b/src/2021/Day08.cpp
@@ -0,0 +1,154 @@
+#include "common/aoc.h"
+
+namespace y2021::day08
+{
+  struct Signal
+  {
+    std::vector<std::set<char>> numbers;
+    std::vector<std::set<char>> display;
+  };
+
+  REGISTER_DAY(2021, Day08, std::vector<Signal>, int);
+
+  REGISTER_TEST_EXAMPLE(2021, Day08, ExampleInput, 1, 26);
+  REGISTER_TEST(2021, Day08, Input, 1, 301);
+  REGISTER_TEST_EXAMPLE(2021, Day08, ExampleInput, 2, 61229);
+  REGISTER_TEST(2021, Day08, Input, 2, 908067);
+
+  READ_INPUT(input)
+  {
+    std::string str;
+    std::vector<Signal> signals;
+    while (getline(input, str))
+    {
+      Signal signal;
+      std::stringstream ss{str};
+      for (int i = 0; i < 10; i++)
+      {
+        std::string s;
+        ss >> s;
+        std::set<char> set;
+        for (char c : s) set.emplace(c);
+        signal.numbers.emplace_back(set);
+      }
+      char c;
+      ss >> c;
+      for (int i = 0; i < 4; i++)
+      {
+        std::string s;
+        ss >> s;
+        std::set<char> set;
+        for (char c : s) set.emplace(c);
+        signal.display.emplace_back(set);
+      }
+      signals.emplace_back(signal);
+    }
+    return signals;
+  }
+
+  OUTPUT1(input)
+  {
+    int count = 0;
+    for (auto&& signal : input)
+    {
+      for (auto&& number : signal.display)
+      {
+        if (number.size() == 2 || number.size() == 3 || number.size() == 4 || number.size() == 7)
+          count++;
+      }
+    }
+    return count;
+  }
+
+  OUTPUT2(input)
+  {
+    int sum = 0;
+    for (auto&& signal : input)
+    {
+      std::vector<std::set<char>> numbers(10);
+      // Find all numbers with unique amount of segments
+      for (auto&& number : signal.numbers)
+      {
+        if (number.size() == 2)
+          numbers[1] = number;
+        if (number.size() == 3)
+          numbers[7] = number;
+        if (number.size() == 4)
+          numbers[4] = number;
+        if (number.size() == 7)
+          numbers[8] = number;
+      }
+
+      // Find all numbers with five and six segments
+      std::vector<std::set<char>> fivesegs;
+      std::vector<std::set<char>> sixsegs;
+      for (auto&& number : signal.numbers)
+      {
+        if (number.size() == 5)
+          fivesegs.emplace_back(number);
+        if (number.size() == 6)
+          sixsegs.emplace_back(number);
+      }
+
+      // Find number 3 (only five segment number which 1 is a subset of)
+      for (auto it = fivesegs.begin(); it != fivesegs.end(); it++)
+      {
+        if (Helper::IsSubset(numbers[1], *it))
+        {
+          numbers[3] = *it;
+          fivesegs.erase(it);
+          break;
+        }
+      }
+
+      // Find number 6 (only six segment number which is not a subset of 1)
+      for (auto it = sixsegs.begin(); it != sixsegs.end(); it++)
+      {
+        if (!Helper::IsSubset(numbers[1], *it))
+        {
+          numbers[6] = *it;
+          sixsegs.erase(it);
+          break;
+        }
+      }
+
+      // Find number 5 (only five segment number which is a subset of 6)
+      for (auto it = fivesegs.begin(); it != fivesegs.end(); it++)
+      {
+        if (Helper::IsSubset(*it, numbers[6]))
+        {
+          numbers[5] = *it;
+          fivesegs.erase(it);
+          break;
+        }
+      }
+      // Find number 2 (last five segment number)
+      numbers[2] = fivesegs.front();
+
+      // Find number 9 (only six segment number which 4 is a subset of)
+      for (auto it = sixsegs.begin(); it != sixsegs.end(); it++)
+      {
+        if (Helper::IsSubset(numbers[4], *it))
+        {
+          numbers[9] = *it;
+          sixsegs.erase(it);
+          break;
+        }
+      }
+
+      // Find number 0 (last six segment number)
+      numbers[0] = sixsegs.front();
+
+      // Calculate the segment display
+      int num = 0;
+      for (auto number : signal.display)
+      {
+        auto it = std::find(numbers.begin(), numbers.end(), number);
+        int i = it - numbers.begin();
+        num = num * 10 + i;
+      }
+      sum += num;
+    }
+    return sum;
+  }
+}
diff --git a/src/2021/Day09.cpp b/src/2021/Day09.cpp
new file mode 100644
index 0000000..2ebfe44
--- /dev/null
+++ b/src/2021/Day09.cpp
@@ -0,0 +1,91 @@
+#include "common/aoc.h"
+
+namespace y2021::day09
+{
+  REGISTER_DAY(2021, Day09, Array2D<int>, int);
+
+  REGISTER_TEST_EXAMPLE(2021, Day09, ExampleInput, 1, 15);
+  REGISTER_TEST(2021, Day09, Input, 1, 478);
+  REGISTER_TEST_EXAMPLE(2021, Day09, ExampleInput, 2, 1134);
+  REGISTER_TEST(2021, Day09, Input, 2, 1327014);
+
+  READ_INPUT(input)
+  {
+    return Input::ReadDigitsAsArray2D(input);
+  }
+
+  OUTPUT1(input)
+  {
+    int count = 0;
+    Index2D index{0, 0};
+    for (auto& val : input)
+    {
+      Index2D indices[4]{
+        {index.x - 1, index.y}, {index.x, index.y - 1}, {index.x + 1, index.y}, {index.x, index.y + 1}};
+      bool all = true;
+      for (auto& ind : indices)
+      {
+        if (input.IsInside(ind) && input[ind] <= val)
+        {
+          all = false;
+          break;
+        }
+      }
+      if (all)
+        count += val + 1;
+      input.Increment(index);
+    }
+    return count;
+  }
+
+  OUTPUT2(input)
+  {
+    std::vector<Index2D> basins;
+    Index2D index{0, 0};
+    for (auto& val : input)
+    {
+      Index2D indices[4]{
+        {index.x - 1, index.y}, {index.x, index.y - 1}, {index.x + 1, index.y}, {index.x, index.y + 1}};
+      bool all = true;
+      for (auto& ind : indices)
+      {
+        if (input.IsInside(ind) && input[ind] <= val)
+        {
+          all = false;
+          break;
+        }
+      }
+      if (all)
+        basins.emplace_back(index);
+      input.Increment(index);
+    }
+
+    std::vector<int> numbers;
+    for (auto&& basin : basins)
+    {
+      std::stack<Index2D> stack;
+      std::set<Index2D> visited;
+      stack.emplace(basin);
+      visited.emplace(basin);
+      while (!stack.empty())
+      {
+        auto index = stack.top();
+        stack.pop();
+        Index2D indices[4]{
+          {index.x - 1, index.y}, {index.x, index.y - 1}, {index.x + 1, index.y}, {index.x, index.y + 1}};
+        for (auto&& ind : indices)
+        {
+          if (input.IsInside(ind) && input[ind] != 9 && visited.find(ind) == visited.end())
+          {
+            stack.emplace(ind);
+            visited.emplace(ind);
+          }
+        }
+      }
+      numbers.emplace_back(visited.size());
+    }
+
+    std::sort(numbers.begin(), numbers.end());
+    return numbers[numbers.size() - 1] * numbers[numbers.size() - 2] * numbers[numbers.size() - 3];
+  }
+}
diff --git a/src/2021/Day10.cpp b/src/2021/Day10.cpp
new file mode 100644
index 0000000..a4ab0d1
--- /dev/null
+++ b/src/2021/Day10.cpp
@@ -0,0 +1,90 @@
+#include "common/aoc.h"
+
+namespace y2021::day10
+{
+  REGISTER_DAY(2021, Day10, std::vector<std::string>, int64_t);
+
+  REGISTER_TEST_EXAMPLE(2021, Day10, ExampleInput, 1, 26397);
+  REGISTER_TEST(2021, Day10, Input, 1, 240123);
+  REGISTER_TEST_EXAMPLE(2021, Day10, ExampleInput, 2, 288957);
+  REGISTER_TEST(2021, Day10, Input, 2, 3260812321);
+
+  READ_INPUT(input)
+  {
+    return Input::ReadLines(input);
+  }
+
+  OUTPUT1(input)
+  {
+    std::map<char, int64_t> values{{')', 3}, {']', 57}, {'}', 1197}, {'>', 25137}};
+    Mapper<char, char> mapper{{'(', ')'}, {'[', ']'}, {'{', '}'}, {'<', '>'}};
+    int64_t count = 0;
+    for (auto&& str : input)
+    {
+      std::stack<char> stack;
+      stack.emplace(str[0]);
+      for (size_t i = 1; i < str.size(); i++)
+      {
+        char* ptr = mapper.GetFirst(str[i]);
+        if (ptr)
+        {
+          if (stack.top() != *ptr)
+          {
+            count += values[str[i]];
+            break;
+          }
+          stack.pop();
+        }
+        else
+        {
+          stack.emplace(str[i]);
+        }
+      }
+    }
+    return count;
+  }
+
+  OUTPUT2(input)
+  {
+    Mapper<char, char> mapper{{'(', ')'}, {'[', ']'}, {'{', '}'}, {'<', '>'}};
+    std::map<char, int64_t> values{{'(', 1}, {'[', 2}, {'{', 3}, {'<', 4}};
+    int64_t count = 0;
+    std::vector<int64_t> scores;
+    for (auto&& str : input)
+    {
+      std::stack<char> stack;
+      stack.emplace(str[0]);
+      bool valid = true;
+      for (size_t i = 1; i < str.size(); i++)
+      {
+        char* ptr = mapper.GetFirst(str[i]);
+        if (ptr)
+        {
+          if (stack.top() != *ptr)
+          {
+            valid = false;
+            break;
+          }
+          stack.pop();
+        }
+        else
+        {
+          stack.emplace(str[i]);
+        }
+      }
+      if (valid)
+      {
+        int64_t score = 0;
+        while (!stack.empty())
+        {
+          score *= 5;
+          score += values[stack.top()];
+          stack.pop();
+        }
+        scores.emplace_back(score);
+      }
+    }
+    std::sort(scores.begin(), scores.end());
+    return scores[scores.size() / 2];
+  }
+}
diff --git a/src/2021/Day11.cpp b/src/2021/Day11.cpp
new file mode 100644
index 0000000..c5fb8df
--- /dev/null
+++ b/src/2021/Day11.cpp
@@ -0,0 +1,82 @@
+#include "common/aoc.h"
+
+namespace y2021::day11
+{
+
+  std::set<Index2D> CalculateFlashing(Array2D<int>& array)
+  {
+    for (auto& val : array) val++;
+    std::set<Index2D> flashed;
+    bool hasChanged = true;
+    while (hasChanged)
+    {
+      Array2D<int> arrayCpy = array;
+      hasChanged = false;
+      Index2D index{0, 0};
+      for (auto& val : array)
+      {
+        if (val > 9 && flashed.find(index) == flashed.end())
+        {
+          flashed.emplace(index);
+          hasChanged = true;
+          for (int y = -1; y < 2; y++)
+          {
+            for (int x = -1; x < 2; x++)
+            {
+              if (x == 0 && y == 0)
+                continue;
+              Index2D newIndex{index.x + x, index.y + y};
+              if (array.IsInside(newIndex))
+                arrayCpy[newIndex]++;
+            }
+          }
+        }
+        array.Increment(index);
+      }
+      array = arrayCpy;
+    }
+    return flashed;
+  }
+
+  REGISTER_DAY(2021, Day11, Array2D<int>, int);
+
+  REGISTER_TEST_EXAMPLE(2021, Day11, ExampleInput, 1, 1656);
+  REGISTER_TEST(2021, Day11, Input, 1, 1667);
+  REGISTER_TEST_EXAMPLE(2021, Day11, ExampleInput, 2, 195);
+  REGISTER_TEST(2021, Day11, Input, 2, 488);
+
+  READ_INPUT(input)
+  {
+    return Input::ReadDigitsAsArray2D(input);
+  }
+
+  OUTPUT1(input)
+  {
+    InputType array = input;
+
+    int count = 0;
+    for (int i = 0; i < 100; i++)
+    {
+      std::set<Index2D> flashed = CalculateFlashing(array);
+      count += flashed.size();
+      for (auto& flash : flashed) array[flash] = 0;
+    }
+    return count;
+  }
+
+  OUTPUT2(input)
+  {
+    InputType array = input;
+
+    int count = 1;
+    while (true)
+    {
+      std::set<Index2D> flashed = CalculateFlashing(array);
+      if (flashed.size() == array.width * array.height)
+        return count;
+      for (auto& flash : flashed) array[flash] = 0;
+      count++;
+    }
+    return count;
+  }
+}
diff --git a/src/2021/Day12.cpp b/src/2021/Day12.cpp
new file mode 100644
index 0000000..c739708
--- /dev/null
+++ b/src/2021/Day12.cpp
@@ -0,0 +1,128 @@
+#include "common/aoc.h"
+
+namespace y2021::day12
+{
+  struct Node
+  {
+    std::set<std::string> connections;
+  };
+
+  struct Path
+  {
+    std::vector<std::string> path{"start"};
+    bool hasDuplicate = false;
+  };
+
+  using NodeMap = std::map<std::string, Node>;
+  REGISTER_DAY(2021, Day12, NodeMap, int);
+
+  REGISTER_TEST_EXAMPLE(2021, Day12, ExampleInput, 1, 10);
+  REGISTER_TEST(2021, Day12, Input, 1, 3887);
+  REGISTER_TEST_EXAMPLE(2021, Day12, ExampleInput, 2, 36);
+  REGISTER_TEST(2021, Day12, Input, 2, 104834);
+
+  READ_INPUT(input)
+  {
+    NodeMap nodes;
+    std::string str;
+    while (getline(input, str))
+    {
+      std::stringstream ss{str};
+      std::string from, to;
+      getline(ss, from, '-');
+      getline(ss, to);
+      auto itFrom = nodes.find(from);
+      auto itTo = nodes.find(to);
+      if (itFrom == nodes.end())
+        itFrom = nodes.emplace(from, Node{}).first;
+      if (itTo == nodes.end())
+        itTo = nodes.emplace(to, Node{}).first;
+
+      itFrom->second.connections.emplace(to);
+      itTo->second.connections.emplace(from);
+    }
+    return nodes;
+  }
+
+  OUTPUT1(input)
+  {
+    int count = 0;
+    std::stack<std::vector<std::string>> paths;
+    paths.emplace(std::vector<std::string>{"start"});
+    while (!paths.empty())
+    {
+      auto path = paths.top();
+      paths.pop();
+      if (path.back() == "end")
+      {
+        count++;
+        continue;
+      }
+      auto it = input.find(path.back());
+      for (auto& connection : it->second.connections)
+      {
+        if (connection[0] >= 'a' && connection[0] <= 'z')
+        {
+          if (std::find(path.begin(), path.end(), connection) == path.end())
+          {
+            std::vector<std::string> cpy = path;
+            cpy.emplace_back(connection);
+            paths.emplace(cpy);
+          }
+        }
+        else
+        {
+          std::vector<std::string> cpy = path;
+          cpy.emplace_back(connection);
+          paths.emplace(cpy);
+        }
+      }
+    }
+    return count;
+  }
+
+  OUTPUT2(input)
+  {
+    int count = 0;
+    std::stack<Path> paths;
+    paths.emplace(Path{});
+    while (!paths.empty())
+    {
+      auto path = paths.top();
+      paths.pop();
+      if (path.path.back() == "end")
+      {
+        count++;
+        continue;
+      }
+
+      auto it = input.find(path.path.back());
+      for (auto& connection : it->second.connections)
+      {
+        if (connection[0] >= 'a' && connection[0] <= 'z')
+        {
+          if (std::find(path.path.begin(), path.path.end(), connection) == path.path.end())
+          {
+            Path cpy = path;
+            cpy.path.emplace_back(connection);
+            paths.emplace(cpy);
+          }
+          else if (!path.hasDuplicate && connection != "start")
+          {
+            Path cpy = path;
+            cpy.path.emplace_back(connection);
+            cpy.hasDuplicate = true;
+            paths.emplace(cpy);
+          }
+        }
+        else
+        {
+          Path cpy = path;
+          cpy.path.emplace_back(connection);
+          paths.emplace(cpy);
+        }
+      }
+    }
+    return count;
+  }
+}
diff --git a/src/2021/Day13.cpp b/src/2021/Day13.cpp
new file mode 100644
index 0000000..885e6e8
--- /dev/null
+++ b/src/2021/Day13.cpp
@@ -0,0 +1,100 @@
+#include "common/aoc.h"
+
+namespace y2021::day13
+{
+
+  void Fold(std::set<Index2D>& indices, bool x, int fold)
+  {
+    std::set<Index2D> newIndices;
+    for (auto& index : indices)
+    {
+      // y axis
+      if (x)
+      {
+        Index2D newIndex = index;
+        if (newIndex.x > fold)
+          newIndex.x = fold - (newIndex.x - 1) % fold - 1;
+        newIndices.emplace(newIndex);
+      }
+      else
+      {
+        Index2D newIndex = index;
+        if (newIndex.y > fold)
+          newIndex.y = fold - (newIndex.y - 1) % fold - 1;
+        newIndices.emplace(newIndex);
+      }
+    }
+    indices = newIndices;
+  }
+
+  struct Paper
+  {
+    std::set<Index2D> indices;
+    std::vector<std::pair<bool, int>> folds;
+  };
+
+  REGISTER_DAY(2021, Day13, Paper, int);
+
+  REGISTER_TEST_EXAMPLE(2021, Day13, ExampleInput, 1, 17);
+  REGISTER_TEST(2021, Day13, Input, 1, 716);
+  REGISTER_TEST_EXAMPLE(2021, Day13, ExampleInput, 2, 16);
+  REGISTER_TEST(2021, Day13, Input, 2, 97);
+
+  READ_INPUT(input)
+  {
+    Paper paper;
+    std::string str;
+    while (getline(input, str))
+    {
+      if (str.empty())
+        break;
+      Index2D index;
+      std::stringstream ss{str};
+      ss >> index.x >> "," >> index.y;
+      paper.indices.emplace(index);
+    }
+
+    while (getline(input, str))
+    {
+      char c, c2;
+      std::string s;
+      int i;
+      std::stringstream ss{str};
+      ss >> s >> s >> c >> c2 >> i;
+      paper.folds.emplace_back(c == 'x', i);
+    }
+    return paper;
+  }
+
+  OUTPUT1(input)
+  {
+    std::set<Index2D> indices = input.indices;
+    Fold(indices, input.folds.front().first, input.folds.front().second);
+    return indices.size();
+  }
+
+  OUTPUT2(input)
+  {
+    std::set<Index2D> indices = input.indices;
+    for (auto& fold : input.folds)
+    {
+      Fold(indices, fold.first, fold.second);
+    }
+
+    Index2D max = *indices.begin();
+    for (auto index : indices)
+    {
+      max.x = std::max(index.x, max.x);
+      max.y = std::max(index.y, max.y);
+    }
+    Array2D<char> board{max.x + 1, max.y + 1};
+    board.Fill(' ');
+    for (auto& index : indices)
+    {
+      board[index] = '#';
+    }
+    std::cout << board;
+    // Not the "correct" output to part 2, but it verifies something at least
+    return indices.size();
+  }
+}
diff --git a/src/2021/Day14.cpp b/src/2021/Day14.cpp
new file mode 100644
index 0000000..8e8cd90
--- /dev/null
+++ b/src/2021/Day14.cpp
@@ -0,0 +1,121 @@
+#include "common/aoc.h"
+
+namespace y2021::day14
+{
+  struct Data
+  {
+    std::string str;
+    std::map<std::string, char> pairs;
+  };
+
+  REGISTER_DAY(2021, Day14, Data, int64_t);
+
+  REGISTER_TEST_EXAMPLE(2021, Day14, ExampleInput, 1, 1588);
+  REGISTER_TEST(2021, Day14, Input, 1, 4517);
+  REGISTER_TEST_EXAMPLE(2021, Day14, ExampleInput, 2, 2188189693529);
+  REGISTER_TEST(2021, Day14, Input, 2, 4704817645083);
+
+  READ_INPUT(input)
+  {
+    Data data;
+    getline(input, data.str);
+    std::string str;
+    getline(input, str);
+
+    while (getline(input, str))
+    {
+      data.pairs.emplace(str.substr(0, 2), str[6]);
+    }
+    return data;
+  }
+
+  OUTPUT1(input)
+  {
+    std::string str = input.str;
+    for (int i = 0; i < 10; i++)
+    {
+      std::string newString;
+      for (size_t j = 0; j < str.size() - 1; j++)
+      {
+        auto it = input.pairs.find(str.substr(j, 2));
+        newString.push_back(str[j]);
+        newString.push_back(it->second);
+      }
+      newString.push_back(str.back());
+      str = newString;
+    }
+    std::map<char, int64_t> occurences;
+    for (char c : str)
+    {
+      occurences[c]++;
+    }
+    int64_t min = occurences.begin()->second;
+    char minChar = occurences.begin()->first;
+    int64_t max = occurences.begin()->second;
+    char maxChar = occurences.begin()->first;
+    for (auto& occurence : occurences)
+    {
+      if (occurence.second < min)
+      {
+        min = occurence.second;
+        minChar = occurence.first;
+      }
+      if (occurence.second > max)
+      {
+        max = occurence.second;
+        maxChar = occurence.first;
+      }
+    }
+    return occurences[maxChar] - occurences[minChar];
+  }
+
+  OUTPUT2(input)
+  {
+    std::string str = input.str;
+    std::map<std::string, int64_t> pairCounts;
+    for (size_t j = 0; j < str.size() - 1; j++)
+    {
+      pairCounts[input.str.substr(j, 2)]++;
+    }
+    for (int i = 0; i < 40; i++)
+    {
+      std::map<std::string, int64_t> cpy = pairCounts;
+      for (auto& pairCount : cpy)
+      {
+        if (pairCount.second <= 0)
+          continue;
+        auto it = input.pairs.find(pairCount.first);
+        std::string firstPair = pairCount.first.substr(0, 1) + it->second;
+        std::string secondPair = it->second + pairCount.first.substr(1, 1);
+        pairCounts[firstPair] += pairCount.second;
+        pairCounts[secondPair] += pairCount.second;
+        pairCounts[pairCount.first] -= pairCount.second;
+      }
+    }
+    std::map<char, int64_t> occurences;
+    for (auto& pairCount : pairCounts)
+    {
+      if (pairCount.second != 0)
+        occurences[pairCount.first[0]] += pairCount.second;
+    }
+    occurences[str.back()]++;
+    int64_t min = occurences.begin()->second;
+    char minChar = occurences.begin()->first;
+    int64_t max = occurences.begin()->second;
+    char maxChar = occurences.begin()->first;
+    for (auto& occurence : occurences)
+    {
+      if (occurence.second < min)
+      {
+        min = occurence.second;
+        minChar = occurence.first;
+      }
+      if (occurence.second > max)
+      {
+        max = occurence.second;
+        maxChar = occurence.first;
+      }
+    }
+    return occurences[maxChar] - occurences[minChar];
+  }
+}
diff --git a/src/2021/Day15.cpp b/src/2021/Day15.cpp
new file mode 100644
index 0000000..6f28287
--- /dev/null
+++ b/src/2021/Day15.cpp
@@ -0,0 +1,63 @@
+#include "common/aoc.h"
+
+namespace y2021::day15
+{
+
+  int Heuristic(const Array2D<int>& array, const Index2D& index)
+  {
+    return std::abs(index.x - array.width + 1) && std::abs(index.y - array.height + 1);
+  }
+
+  std::vector<std::pair<int, Index2D>> Branch(const Array2D<int>& array, const Index2D& index)
+  {
+    Index2D indices[4]{{index.x - 1, index.y}, {index.x, index.y - 1}, {index.x + 1, index.y}, {index.x, index.y + 1}};
+    std::vector<std::pair<int, Index2D>> moves;
+    for (auto& index : indices)
+    {
+      if (array.IsInside(index))
+        moves.emplace_back(std::pair<int, Index2D>{array[index], index});
+    }
+    return moves;
+  }
+
+  int Goal(const Array2D<int>& array, const Index2D& index)
+  {
+    return index.x == array.width - 1 && index.y == array.height - 1;
+  }
+
+  int Pathfinder(const Array2D<int>& array)
+  {
+    return Helper::AStar(array, Index2D{0, 0}, Heuristic, Branch, Goal);
+  }
+
+  REGISTER_DAY(2021, Day15, Array2D<int>, int);
+
+  REGISTER_TEST_EXAMPLE(2021, Day15, ExampleInput, 1, 40);
+  REGISTER_TEST(2021, Day15, Input, 1, 714);
+  REGISTER_TEST_EXAMPLE(2021, Day15, ExampleInput, 2, 315);
+  REGISTER_TEST(2021, Day15, Input, 2, 2948);
+
+  READ_INPUT(input)
+  {
+    return Input::ReadDigitsAsArray2D(input);
+  }
+
+  OUTPUT1(input)
+  {
+    return Pathfinder(input);
+  }
+
+  OUTPUT2(input)
+  {
+    Array2D<int> array{input.width * 5, input.height * 5};
+    Index2D index{0, 0};
+    for (auto& val : array)
+    {
+      val = input.GetMod(index.x, index.y) + index.x / input.width + index.y / input.height;
+      if (val >= 10)
+        val = val % 10 + 1;
+      array.Increment(index);
+    }
+    return Pathfinder(array);
+  }
+}
diff --git a/src/2021/Day16.cpp b/src/2021/Day16.cpp
new file mode 100644
index 0000000..1348867
--- /dev/null
+++ b/src/2021/Day16.cpp
@@ -0,0 +1,128 @@
+#include "common/aoc.h"
+
+namespace y2021::day16
+{
+  int64_t Read(const std::string& str, int& offset, int size)
+  {
+    int64_t i = Helper::BinStrToInt64(str.substr(offset, size));
+    offset += size;
+    return i;
+  }
+
+  std::pair<int64_t, int64_t> ReadPacket(const std::string& str, int& offset)
+  {
+    int64_t version = Read(str, offset, 3);
+    int64_t type = Read(str, offset, 3);
+
+    if (type == 4)
+    {
+      // Normal packet
+      int64_t type = Read(str, offset, 1);
+      int64_t val = 0;
+      while (type == 1)
+      {
+        val = (val << 4) | Read(str, offset, 4);
+        type = Read(str, offset, 1);
+      }
+      val = (val << 4) | Read(str, offset, 4);
+      return {version, val};
+    }
+    else
+    {
+      // Packet containing packets
+      int64_t lengthId = Read(str, offset, 1);
+      std::vector<int64_t> values;
+      int64_t versionTotal = version;
+      if (lengthId == 0)
+      {
+        int64_t totalLength = Read(str, offset, 15);
+        int64_t start = offset;
+        while (offset < start + totalLength)
+        {
+          auto [version, value] = ReadPacket(str, offset);
+          values.emplace_back(value);
+          versionTotal += version;
+        }
+      }
+      else
+      {
+        int64_t totalPackets = Read(str, offset, 11);
+        for (int64_t i = 0; i < totalPackets; i++)
+        {
+          auto [version, value] = ReadPacket(str, offset);
+          values.emplace_back(value);
+          versionTotal += version;
+        }
+      }
+
+      if (type == 0)
+        return {versionTotal,
+                std::accumulate(values.begin(), values.end(), 0ll, [](int64_t sum, int64_t val) { return sum + val; })};
+      else if (type == 1)
+        return {
+          versionTotal,
+          std::accumulate(values.begin(), values.end(), 1ll, [](int64_t prod, int64_t val) { return prod * val; })};
+      else if (type == 2)
+        return {
+          versionTotal,
+          std::accumulate(
+            values.begin(), values.end(), values.front(), [](int64_t max, int64_t val) { return std::min(max, val); })};
+      else if (type == 3)
+        return {
+          versionTotal,
+          std::accumulate(
+            values.begin(), values.end(), values.front(), [](int64_t min, int64_t val) { return std::max(min, val); })};
+      else if (type == 5)
+        return {versionTotal, values[0] > values[1] ? 1 : 0};
+      else if (type == 6)
+        return {versionTotal, values[0] < values[1] ? 1 : 0};
+      else if (type == 7)
+        return {versionTotal, values[0] == values[1] ? 1 : 0};
+    }
+    return {0, 0};
+  }
+
+  std::pair<int64_t, int64_t> ReadPacket(const std::string& str)
+  {
+    int offset = 0;
+    return ReadPacket(str, offset);
+  }
+
+  REGISTER_DAY(2021, Day16, std::string, int64_t);
+
+  REGISTER_TEST_EXAMPLE(2021, Day16, ExampleInput, 1, 20);
+  REGISTER_TEST(2021, Day16, Input, 1, 984);
+  REGISTER_TEST_EXAMPLE(2021, Day16, ExampleInput, 2, 1);
+  REGISTER_TEST(2021, Day16, Input, 2, 1015320896946);
+
+  READ_INPUT(input)
+  {
+    std::string str;
+    getline(input, str);
+    std::string bin;
+    for (char c : str)
+    {
+      if (c >= '0' && c <= '9')
+      {
+        char val = c - '0';  // vs compiler throws warnings if this is inlined into the bitset function...
+        bin += std::bitset<4>(val).to_string();
+      }
+      else if (c >= 'A' && c <= 'F')
+      {
+        char val = c - 'A' + 10;  // vs compiler throws warnings if this is inlined into the bitset function...
+        bin += std::bitset<4>(val).to_string();
+      }
+    }
+    return bin;
+  }
+
+  OUTPUT1(input)
+  {
+    return ReadPacket(input).first;
+  }
+
+  OUTPUT2(input)
+  {
+    return ReadPacket(input).second;
+  }
+}
diff --git a/src/2021/Day17.cpp b/src/2021/Day17.cpp
new file mode 100644
index 0000000..dcfeb1b
--- /dev/null
+++ b/src/2021/Day17.cpp
@@ -0,0 +1,61 @@
+#include "common/aoc.h"
+
+namespace y2021::day17
+{
+  struct Area
+  {
+    Index2D p1;
+    Index2D p2;
+  };
+
+  REGISTER_DAY(2021, Day17, Area, int);
+
+  REGISTER_TEST_EXAMPLE(2021, Day17, ExampleInput, 1, 45);
+  REGISTER_TEST(2021, Day17, Input, 1, 2701);
+  REGISTER_TEST_EXAMPLE(2021, Day17, ExampleInput, 2, 112);
+  REGISTER_TEST(2021, Day17, Input, 2, 1070);
+
+  READ_INPUT(input)
+  {
+    Area area;
+    input >> "target area: x=" >> area.p1.x >> ".." >> area.p2.x >> ", y=" >> area.p1.y >> ".." >> area.p2.y;
+    return area;
+  }
+
+  OUTPUT1(input)
+  {
+    int v = -input.p1.y;
+    return v * (v - 1) / 2;
+  }
+
+  OUTPUT2(input)
+  {
+    int count = 0;
+    for (int y = input.p1.y - 1; y <= -input.p1.y; y++)
+    {
+      for (int x = 1; x <= input.p2.x; x++)
+      {
+        int xPos = 0;
+        int yPos = 0;
+
+        int vx = x;
+        int vy = y;
+        while (xPos <= input.p2.x && yPos >= input.p1.y)
+        {
+          if (xPos >= input.p1.x && xPos <= input.p2.x && yPos >= input.p1.y && yPos <= input.p2.y)
+          {
+            count++;
+            break;
+          }
+          xPos += vx;
+          yPos += vy;
+          vx--;
+          if (vx < 0)
+            vx = 0;
+          vy--;
+        }
+      }
+    }
+    return count;
+  }
+}
diff --git a/src/2021/Day18.cpp b/src/2021/Day18.cpp
new file mode 100644
index 0000000..b0b07a5
--- /dev/null
+++ b/src/2021/Day18.cpp
@@ -0,0 +1,323 @@
+#include "common/aoc.h"
+
+namespace y2021::day18
+{
+  struct Node
+  {
+    Node* parent = nullptr;
+    int value = 0;
+    std::vector<Node> nodes;
+
+    Node() = default;
+
+    Node(const std::string& str)
+      : nodes{Node{}, Node{}}
+    {
+      UpdateParents();
+      std::stringstream ss{str};
+      ss >> *this;
+    }
+
+    Node(int value)
+      : value{value}
+    {
+    }
+
+    Node(const Node& left, const Node& right)
+      : nodes{left, right}
+    {
+      UpdateParents();
+    }
+
+    Node& Left()
+    {
+      return nodes[0];
+    }
+
+    const Node& Left() const
+    {
+      return nodes[0];
+    }
+
+    Node& Right()
+    {
+      return nodes[1];
+    }
+
+    const Node& Right() const
+    {
+      return nodes[1];
+    }
+
+    bool IsNumber() const
+    {
+      return nodes.size() == 0;
+    }
+
+    int& Number()
+    {
+      return value;
+    }
+
+    int Number() const
+    {
+      return value;
+    }
+
+    int Calculate()
+    {
+      int i = 0;
+      if (Left().IsNumber())
+        i += 3 * Left().Number();
+      else
+        i += 3 * Left().Calculate();
+
+      if (Right().IsNumber())
+        i += 2 * Right().Number();
+      else
+        i += 2 * Right().Calculate();
+      return i;
+    }
+
+    void AddToLeft(int value, Node* from)
+    {
+      if (Left().IsNumber())
+        Left().Number() += value;
+      else
+      {
+        Node& node = Left();
+        if (&node == from)
+        {
+          if (parent != nullptr)
+            parent->AddToLeft(value, this);
+        }
+        else
+          node.AddToRightDown(value);
+      }
+    }
+
+    void AddToRightDown(int value)
+    {
+      if (Right().IsNumber())
+        Right().Number() += value;
+      else
+      {
+        Right().AddToRightDown(value);
+      }
+    }
+
+    void AddToRight(int value, Node* from)
+    {
+      if (Right().IsNumber())
+        Right().Number() += value;
+      else
+      {
+        Node& node = Right();
+        if (&node == from)
+        {
+          if (parent != nullptr)
+            parent->AddToRight(value, this);
+        }
+        else
+          node.AddToLeftDown(value);
+      }
+    }
+
+    void AddToLeftDown(int value)
+    {
+      if (Left().IsNumber())
+        Left().Number() += value;
+      else
+      {
+        Left().AddToLeftDown(value);
+      }
+    }
+
+    bool Explode(int depth = 0)
+    {
+      if (depth >= 4)
+      {
+        parent->AddToLeft(Left().Number(), this);
+        parent->AddToRight(Right().Number(), this);
+
+        if (!parent->Left().IsNumber() && &parent->Left() == this)
+          parent->Left() = 0;
+        if (!parent->Right().IsNumber() && &parent->Right() == this)
+          parent->Right() = 0;
+        return true;
+      }
+      if (!Left().IsNumber())
+        if (Left().Explode(depth + 1))
+          return true;
+      if (!Right().IsNumber())
+        if (Right().Explode(depth + 1))
+          return true;
+      return false;
+    }
+
+    bool Split()
+    {
+      if (!Left().IsNumber())
+      {
+        if (Left().Split())
+          return true;
+      }
+      else if (Left().Number() >= 10)
+      {
+        int val = Left().Number();
+        Node node{(val >> 1), (val >> 1) + (val % 2)};
+        node.parent = this;
+        Left() = node;
+        return true;
+      }
+
+      if (!Right().IsNumber())
+      {
+        if (Right().Split())
+          return true;
+      }
+      else if (Right().Number() >= 10)
+      {
+        int val = Right().Number();
+        Node node{(val >> 1), (val >> 1) + (val % 2)};
+        node.parent = this;
+        Right() = node;
+        return true;
+      }
+      return false;
+    }
+
+    void UpdateParents()
+    {
+      if (!Left().IsNumber())
+      {
+        Left().parent = this;
+        Left().UpdateParents();
+      }
+      if (!Right().IsNumber())
+      {
+        Right().parent = this;
+        Right().UpdateParents();
+      }
+    }
+
+    void Print(std::ostream& stream, int depth) const
+    {
+      std::vector<char> depthStart{'|', '<', '{', '(', '['};
+      std::vector<char> depthEnd{'|', '>', '}', ')', ']'};
+      stream << depthStart[depth];
+      if (Left().IsNumber())
+        stream << Left().Number();
+      else
+        Left().Print(stream, depth + 1);
+      stream << ",";
+      if (Right().IsNumber())
+        stream << Right().Number();
+      else
+        Right().Print(stream, depth + 1);
+      stream << depthEnd[depth];
+    }
+
+    void operator=(int value)
+    {
+      nodes.clear();
+      this->value = value;
+    }
+
+    friend std::ostream& operator<<(std::ostream& stream, const Node& node)
+    {
+      node.Print(stream, 0);
+      return stream;
+    }
+
+    friend std::istream& operator>>(std::istream& stream, Node& node)
+    {
+      stream >> "[";
+      if (stream.peek() == '[')
+      {
+        Node left{Node{}, Node{}};
+        stream >> left;
+        left.parent = &node;
+        node.Left() = left;
+      }
+      else
+      {
+        int i;
+        stream >> i;
+        node.Left() = i;
+      }
+      stream >> ",";
+      if (stream.peek() == '[')
+      {
+        Node right{Node{}, Node{}};
+        stream >> right;
+        right.parent = &node;
+        node.Right() = right;
+      }
+      else
+      {
+        int i;
+        stream >> i;
+        node.Right() = i;
+      }
+      stream >> "]";
+      return stream;
+    }
+  };
+
+  Node Reduce(const Node& lhs, const Node& rhs)
+  {
+    Node node{lhs, rhs};
+    bool changed = true;
+    while (changed)
+    {
+      changed = false;
+      while (node.Explode()) changed = true;
+      if (node.Split())
+        changed = true;
+    }
+    return node;
+  }
+
+  REGISTER_DAY(2021, Day18, std::vector<Node>, int);
+
+  REGISTER_TEST_EXAMPLE(2021, Day18, ExampleInput, 1, 4140);
+  REGISTER_TEST(2021, Day18, Input, 1, 4137);
+  REGISTER_TEST_EXAMPLE(2021, Day18, ExampleInput, 2, 3993);
+  REGISTER_TEST(2021, Day18, Input, 2, 4573);
+
+  READ_INPUT(input)
+  {
+    std::vector<Node> nodes;
+    std::string str;
+    while (getline(input, str))
+    {
+      nodes.emplace_back(str);
+    }
+    return nodes;
+  }
+
+  OUTPUT1(input)
+  {
+    Node node = input[0];
+    for (size_t i = 1; i < input.size(); i++)
+    {
+      node = Reduce(node, input[i]);
+    }
+    return node.Calculate();
+  }
+
+  OUTPUT2(input)
+  {
+    int max = 0;
+    for (size_t i = 0; i < input.size() - 1; i++)
+    {
+      for (size_t j = 1; j < input.size(); j++)
+      {
+        max = std::max(max, Reduce(input[j], input[i]).Calculate());
+        max = std::max(max, Reduce(input[i], input[j]).Calculate());
+      }
+    }
+    return max;
+  }
+}
diff --git a/src/2021/Day19.cpp b/src/2021/Day19.cpp
new file mode 100644
index 0000000..138e672
--- /dev/null
+++ b/src/2021/Day19.cpp
@@ -0,0 +1,278 @@
+#include "common/aoc.h"
+
+namespace y2021::day19
+{
+  constexpr int MAX_ORIENTATIONS = 24;
+  constexpr int MIN_OVERLAP = 12;
+
+  struct Scanner
+  {
+    std::set<Index3D> beacons;
+  };
+
+  struct Overlap
+  {
+    bool overlapping = false;
+    int orientation = 0;
+    Index3D offset{0, 0};
+
+    friend std::ostream& operator<<(std::ostream& stream, const Overlap& overlap)
+    {
+      if (overlap.overlapping)
+        return stream << "true " << overlap.orientation << " " << overlap.offset;
+      else
+        return stream << "false";
+    }
+
+    operator bool()
+    {
+      return overlapping;
+    }
+  };
+
+  Index3D RotateY(const Index3D& index)
+  {
+    return Index3D{-index.z, index.y, index.x};
+  }
+
+  Index3D RotateY2(const Index3D& index)
+  {
+    return Index3D{-index.x, index.y, -index.z};
+  }
+
+  Index3D RotateY3(const Index3D& index)
+  {
+    return Index3D{index.z, index.y, -index.x};
+  }
+
+  Index3D RotateX(const Index3D& index)
+  {
+    return Index3D{index.x, -index.z, index.y};
+  }
+
+  Index3D RotateX2(const Index3D& index)
+  {
+    return Index3D{index.x, -index.y, -index.z};
+  }
+
+  Index3D RotateX3(const Index3D& index)
+  {
+    return Index3D{index.x, index.z, -index.y};
+  }
+
+  Index3D RotateZ(const Index3D& index)
+  {
+    return Index3D{-index.y, index.x, index.z};
+  }
+
+  Index3D RotateZ2(const Index3D& index)
+  {
+    return Index3D{-index.x, -index.y, index.z};
+  }
+
+  Index3D RotateZ3(const Index3D& index)
+  {
+    return Index3D{index.y, -index.x, index.z};
+  }
+
+  Index3D Orient(const Index3D& index, int i)
+  {
+    switch (i)
+    {
+      // Facing forward
+      case 0:
+        return index;
+      case 1:
+        return RotateZ(index);
+      case 2:
+        return RotateZ2(index);
+      case 3:
+        return RotateZ3(index);
+
+      // Facing left
+      case 4:
+        return RotateY(index);
+      case 5:
+        return RotateX(RotateY(index));
+      case 6:
+        return RotateX2(RotateY(index));
+      case 7:
+        return RotateX3(RotateY(index));
+
+      // Facing backward
+      case 8:
+        return RotateY2(index);
+      case 9:
+        return RotateZ(RotateY2(index));
+      case 10:
+        return RotateZ2(RotateY2(index));
+      case 11:
+        return RotateZ3(RotateY2(index));
+
+      // Facing right
+      case 12:
+        return RotateY3(index);
+      case 13:
+        return RotateX(RotateY3(index));
+      case 14:
+        return RotateX2(RotateY3(index));
+      case 15:
+        return RotateX3(RotateY3(index));
+
+      // Facing down
+      case 16:
+        return RotateX(index);
+      case 17:
+        return RotateY(RotateX(index));
+      case 18:
+        return RotateY2(RotateX(index));
+      case 19:
+        return RotateY3(RotateX(index));
+
+      // Facing up
+      case 20:
+        return RotateX3(index);
+      case 21:
+        return RotateY(RotateX3(index));
+      case 22:
+        return RotateY2(RotateX3(index));
+      case 23:
+        return RotateY3(RotateX3(index));
+    }
+    std::cout << "Invalid orientation: " << i << std::endl;
+    return index;
+  }
+
+  Overlap IsOverlapping(const std::set<Index3D>& layout, const Scanner& scanner)
+  {
+    for (auto& index : layout)
+    {
+      int beaconsLeft = scanner.beacons.size();
+      for (auto it = scanner.beacons.begin(); it != scanner.beacons.end(); it++)
+      {
+        if (beaconsLeft < MIN_OVERLAP)
+          break;
+        beaconsLeft--;
+
+        for (int i = 0; i < MAX_ORIENTATIONS; i++)
+        {
+          Index3D offset = index - Orient(*it, i);
+          int count = 0;
+          for (auto it2 = scanner.beacons.begin(); it2 != scanner.beacons.end(); it2++)
+          {
+            if (layout.count(offset + Orient(*it2, i)))
+            {
+              count++;
+            }
+          }
+          if (count >= MIN_OVERLAP)
+            return {true, i, offset};
+        }
+      }
+    }
+    return {false, 0, Index3D{0, 0}};
+  }
+
+  std::pair<int, int> Solve(std::vector<Scanner> scanners)
+  {
+    // Find first overlap to initialize the "correct" layout
+    std::set<Index3D> layout;
+    for (auto it = scanners.begin(); it != scanners.end(); it++)
+    {
+      bool found = false;
+      for (auto it2 = it; it2 != scanners.end(); it2++)
+      {
+        if (it == it2)
+          continue;
+        Overlap overlap = IsOverlapping(it->beacons, *it2);
+        if (overlap)
+        {
+          layout = it->beacons;
+          scanners.erase(it);
+          found = true;
+          break;
+        }
+      }
+      if (found)
+        break;
+    }
+
+    // Find overlapping scanners one by one
+    std::vector<Index3D> scannerPos{Index3D{0, 0, 0}};
+    while (!scanners.empty())
+    {
+      bool removed = false;
+      for (auto it = scanners.begin(); it != scanners.end(); it++)
+      {
+        Overlap overlap = IsOverlapping(layout, *it);
+        if (overlap)
+        {
+          for (auto& beacon : it->beacons)
+          {
+            layout.emplace(overlap.offset + Orient(beacon, overlap.orientation));
+          }
+          scannerPos.emplace_back(overlap.offset);
+          scanners.erase(it);
+          removed = true;
+          break;
+        }
+      }
+      if (!removed)
+      {
+        std::cout << "Could not find position of any remaining scanners" << std::endl;
+        break;
+      }
+    }
+
+    // Find largest manhattan distance between two scanners
+    int maxDistance = 0;
+    for (size_t i = 0; i < scannerPos.size(); i++)
+    {
+      for (size_t j = i + 1; j < scannerPos.size(); j++)
+      {
+        Index3D distance = scannerPos[i] - scannerPos[j];
+        maxDistance = std::max(maxDistance, std::abs(distance.x) + std::abs(distance.y) + std::abs(distance.z));
+      }
+    }
+    return {layout.size(), maxDistance};
+  }
+
+  REGISTER_DAY(2021, Day19, std::vector<Scanner>, int);
+
+  REGISTER_TEST_EXAMPLE(2021, Day19, ExampleInput, 1, 79);
+  REGISTER_TEST(2021, Day19, Input, 1, 359);
+  REGISTER_TEST_EXAMPLE(2021, Day19, ExampleInput, 2, 3621);
+  REGISTER_TEST(2021, Day19, Input, 2, 12292);
+
+  READ_INPUT(input)
+  {
+    std::vector<Scanner> scanners;
+    std::string str;
+    while (getline(input, str))
+    {
+      Scanner scanner;
+      getline(input, str);
+      while (!str.empty())
+      {
+        std::stringstream ss{str};
+        Index3D index;
+        ss >> index.x >> "," >> index.y >> "," >> index.z;
+        scanner.beacons.emplace(index);
+        str.clear();
+        getline(input, str);
+      }
+      scanners.emplace_back(scanner);
+    }
+    return scanners;
+  }
+
+  OUTPUT1(input)
+  {
+    return Solve(input).first;
+  }
+
+  OUTPUT2(input)
+  {
+    return Solve(input).second;
+  }
+}
diff --git a/src/2021/Day20.cpp b/src/2021/Day20.cpp
new file mode 100644
index 0000000..52a6dde
--- /dev/null
+++ b/src/2021/Day20.cpp
@@ -0,0 +1,86 @@
+#include "common/aoc.h"
+
+namespace y2021::day20
+{
+  struct Data
+  {
+    std::string line;
+    Array2D<char> grid;
+  };
+
+  int GetNumber(const Array2D<char>& array, Index2D index)
+  {
+    int num = 0;
+    for (int y = index.y - 1; y <= index.y + 1; y++)
+    {
+      for (int x = index.x - 1; x <= index.x + 1; x++)
+      {
+        num <<= 1;
+        Index2D newIndex{x, y};
+        if (array.IsInside(newIndex) && array[newIndex] == '#')
+          num |= 1;
+      }
+    }
+    return num;
+  }
+
+  int Solve(const Data& input, int iter)
+  {
+    int SIZE = (2 * iter) * 2;
+    Array2D<char> output{input.grid.width + SIZE, input.grid.height + SIZE};
+    Index2D index{0, 0};
+    output.Fill('.');
+    for (auto& val : input.grid)
+    {
+      output.Set(index.x + SIZE / 2, index.y + SIZE / 2, val);
+      input.grid.Increment(index);
+    }
+    for (int i = 0; i < iter; i++)
+    {
+      Array2D<char> cpy = output;
+      Index2D index{0, 0};
+      for (auto& grid : output)
+      {
+        int num = GetNumber(cpy, index);
+        output[index] = input.line[num];
+        output.Increment(index);
+      }
+      std::string str;
+    }
+
+    int count = 0;
+    for (int y = iter; y < output.height - iter; y++)
+      for (int x = iter; x < output.width - iter; x++)
+        if (output.Get(x, y) == '#')
+          count++;
+
+    return count;
+  }
+
+  REGISTER_DAY(2021, Day20, Data, int);
+
+  REGISTER_TEST_EXAMPLE(2021, Day20, ExampleInput, 1, 35);
+  REGISTER_TEST(2021, Day20, Input, 1, 5203);
+  REGISTER_TEST_EXAMPLE(2021, Day20, ExampleInput, 2, 3351);
+  REGISTER_TEST(2021, Day20, Input, 2, 18806);
+
+  READ_INPUT(input)
+  {
+    Data data;
+    std::getline(input, data.line);
+    std::string str;
+    getline(input, str);
+    data.grid = Input::ReadArray2D(input);
+    return data;
+  }
+
+  OUTPUT1(input)
+  {
+    return Solve(input, 2);
+  }
+
+  OUTPUT2(input)
+  {
+    return Solve(input, 50);
+  }
+}
diff --git a/src/2021/Day21.cpp b/src/2021/Day21.cpp
new file mode 100644
index 0000000..c8c33d7
--- /dev/null
+++ b/src/2021/Day21.cpp
@@ -0,0 +1,107 @@
+#include "common/aoc.h"
+
+namespace y2021::day21
+{
+
+  int Mod(int i)
+  {
+    return (i - 1) % 10 + 1;
+  }
+
+  std::pair<int64_t, int64_t> Roll(int position1, int points1, int position2, int points2, bool player1, int depth)
+  {
+    if (points2 >= 21)
+      return {0, 1};
+    else if (points1 >= 21)
+      return {1, 0};
+
+    // 3: 111
+    // 4: 211 121 112
+    // 5: 221 212 122 311 131 113
+    // 6: 222 321 312 213 231 123 132
+    // 7: 223 232 323 133 331 313
+    // 8: 233 323 322
+    // 9: 333
+    std::map<int, int> outcomes{{3, 1}, {4, 3}, {5, 6}, {6, 7}, {7, 6}, {8, 3}, {9, 1}};
+
+    std::pair<int64_t, int64_t> wins{0, 0};
+    int initialPos = 0;
+    int initialPoints = 0;
+    if (player1)
+    {
+      initialPos = position1;
+      initialPoints = points1;
+    }
+    else
+    {
+      initialPos = position2;
+      initialPoints = points2;
+    }
+    for (auto [value, times] : outcomes)
+    {
+      if (player1)
+      {
+        position1 = initialPos;
+        points1 = initialPoints;
+        position1 = Mod(position1 + value);
+        points1 += position1;
+      }
+      else
+      {
+        position2 = initialPos;
+        points2 = initialPoints;
+        position2 = Mod(position2 + value);
+        points2 += position2;
+      }
+      auto subwins = Roll(position1, points1, position2, points2, !player1, depth + 1);
+      wins.first += times * subwins.first;
+      wins.second += times * subwins.second;
+    }
+    return wins;
+  }
+
+  REGISTER_DAY(2021, Day21, std::vector<int>, int64_t);
+
+  REGISTER_TEST_EXAMPLE(2021, Day21, ExampleInput, 1, 739785);
+  REGISTER_TEST(2021, Day21, Input, 1, 503478);
+  REGISTER_TEST_EXAMPLE(2021, Day21, ExampleInput, 2, 444356092776315);
+  REGISTER_TEST(2021, Day21, Input, 2, 716241959649754);
+
+  READ_INPUT(input)
+  {
+    std::vector<int> players;
+    int i;
+    std::string str;
+    while (getline(input, str))
+    {
+      std::stringstream ss{str};
+      ss >> "Player" >> i >> "starting position:" >> i;
+      players.emplace_back(i);
+    }
+    return players;
+  }
+
+  OUTPUT1(input)
+  {
+    std::vector<int> positions = input;
+    std::vector<int> points;
+    points.resize(input.size());
+    for (int i = 1; i < 10000; i += 3)
+    {
+      int index = (i - 1) % 2;
+      positions[index] = Mod(positions[index] + 3 * (i + 1));
+      points[index] += positions[index];
+      if (points[index] >= 1000)
+      {
+        return ((int64_t)i + 2ll) * (int64_t)points[(index + 1) % 2];
+      }
+    }
+    return 0;
+  }
+
+  OUTPUT2(input)
+  {
+    std::pair<int64_t, int64_t> wins = Roll(input[0], 0, input[1], 0, true, 0);
+    return std::max(wins.first, wins.second);
+  }
+}
diff --git a/src/2021/Day22.cpp b/src/2021/Day22.cpp
new file mode 100644
index 0000000..de73517
--- /dev/null
+++ b/src/2021/Day22.cpp
@@ -0,0 +1,138 @@
+#include "common/aoc.h"
+
+namespace y2021::day22
+{
+
+  struct Overlap;
+
+  struct Volume
+  {
+    int sign = 0;
+    Index3D min = Index3D{0, 0};
+    Index3D max = Index3D{0, 0};
+
+    Volume()
+    {
+    }
+
+    Volume(int sign, const Index3D& min, const Index3D& max)
+      : sign{sign},
+        min{min},
+        max{max}
+    {
+    }
+
+    int64_t GetCubes() const
+    {
+      return ((int64_t)max.x - (int64_t)min.x + 1ll) * ((int64_t)max.y - (int64_t)min.y + 1ll) *
+             ((int64_t)max.z - (int64_t)min.z + 1ll);
+    }
+
+    Overlap GetOverlap(const Volume& other) const;
+
+    friend std::ostream& operator<<(std::ostream& stream, const Volume& volume)
+    {
+      return stream << volume.min << " " << volume.max;
+    }
+  };
+
+  struct Overlap
+  {
+    bool overlap = false;
+    Volume volume;
+
+    Overlap(bool overlap, const Volume& volume)
+      : overlap{overlap},
+        volume{volume}
+    {
+    }
+
+    operator bool()
+    {
+      return overlap;
+    }
+  };
+
+  Overlap Volume::GetOverlap(const Volume& other) const
+  {
+    if (min.x > other.max.x || min.y > other.max.y || min.z > other.max.z || max.x < other.min.x ||
+        max.y < other.min.y || max.z < other.min.z)
+      return Overlap{false, Volume{0, Index3D{}, Index3D{}}};
+
+    return Overlap{
+      true,
+      Volume{-other.sign,
+             Index3D{std::max(min.x, other.min.x), std::max(min.y, other.min.y), std::max(min.z, other.min.z)},
+             Index3D{std::min(max.x, other.max.x), std::min(max.y, other.max.y), std::min(max.z, other.max.z)}}};
+  }
+
+  REGISTER_DAY(2021, Day22, std::vector<Volume>, int64_t);
+
+  REGISTER_TEST_EXAMPLE(2021, Day22, ExampleInput, 1, 474140);
+  REGISTER_TEST(2021, Day22, Input, 1, 596598);
+  REGISTER_TEST_EXAMPLE(2021, Day22, ExampleInput, 2, 2758514936282235);
+  REGISTER_TEST(2021, Day22, Input, 2, 1199121349148621);
+
+  READ_INPUT(input)
+  {
+    std::vector<Volume> volumes;
+    std::string str;
+    while (getline(input, str))
+    {
+      Volume volume;
+      std::stringstream ss{str};
+      std::string s;
+      ss >> s >> "x=" >> volume.min.x >> ".." >> volume.max.x >> "," >> "y=" >> volume.min.y >> ".." >> volume.max.y >>
+        "," >> "z=" >> volume.min.z >> ".." >> volume.max.z;
+      volume.sign = s == "on" ? 1 : -1;
+      volumes.emplace_back(volume);
+    }
+    return volumes;
+  }
+
+  OUTPUT1(input)
+  {
+    Array3D<char> values{101, 101, 101};
+    values.Fill('.');
+    for (auto& region : input)
+    {
+      for (int z = std::max(region.min.z, -50); z <= std::min(region.max.z, 50); z++)
+      {
+        for (int y = std::max(region.min.y, -50); y <= std::min(region.max.y, 50); y++)
+        {
+          for (int x = std::max(region.min.x, -50); x <= std::min(region.max.x, 50); x++)
+          {
+            if (values.IsInside(Index3D{x + 50, y + 50, z + 50}))
+            {
+              values.Set(x + 50, y + 50, z + 50, region.sign > 0 ? '#' : '.');
+            }
+          }
+        }
+      }
+    }
+    return values.Count('#');
+  }
+
+  OUTPUT2(input)
+  {
+    std::vector<Volume> volumes;
+    for (auto& volume : input)
+    {
+      size_t size = volumes.size();
+      for (size_t i = 0; i < size; i++)
+      {
+        Overlap overlap = volume.GetOverlap(volumes[i]);
+        if (overlap)
+        {
+          volumes.emplace_back(overlap.volume);
+        }
+      }
+      if (volume.sign > 0)
+      {
+        volumes.emplace_back(volume);
+      }
+    }
+    return Helper::Sum<int64_t>(volumes,
+                                [](int64_t sum, const Volume& vol) { return sum + vol.GetCubes() * vol.sign; });
+  }
+}
diff --git a/src/2021/Day23.cpp b/src/2021/Day23.cpp
new file mode 100644
index 0000000..ed369f3
--- /dev/null
+++ b/src/2021/Day23.cpp
@@ -0,0 +1,243 @@
+#include "common/aoc.h"
+
+namespace y2021::day23
+{
+
+  using State = std::map<Index2D, char>;
+
+  bool Find(const State& state, const Index2D& pos, char c)
+  {
+    auto it = state.find(pos);
+    if (it != state.end())
+      return it->second == c;
+    return false;
+  }
+
+  bool ValidateState(int height, const State& state)
+  {
+    return Find(state, {2, 1}, 'A') && Find(state, {2, 2}, 'A') && Find(state, {4, 1}, 'B') &&
+           Find(state, {4, 2}, 'B') && Find(state, {6, 1}, 'C') && Find(state, {6, 2}, 'C') &&
+           Find(state, {8, 1}, 'D') && Find(state, {8, 2}, 'D');
+  }
+
+  int Heuristic(int height, const State& state)
+  {
+    int h = 0;
+    for (auto& piece : state)
+    {
+      // Cost to move piece to the top of the room
+      if (piece.second == 'A' && piece.first.x != 2)
+        h += std::abs(piece.first.x - 2) + std::abs(piece.first.y - 0) + 1;
+      if (piece.second == 'B' && piece.first.x != 4)
+        h += (std::abs(piece.first.x - 4) + std::abs(piece.first.y - 0) + 1) * 10;
+      if (piece.second == 'C' && piece.first.x != 6)
+        h += (std::abs(piece.first.x - 6) + std::abs(piece.first.y - 0) + 1) * 100;
+      if (piece.second == 'D' && piece.first.x != 8)
+        h += (std::abs(piece.first.x - 8) + std::abs(piece.first.y - 0) + 1) * 1000;
+    }
+    return h;
+  }
+
+  int GetCost(char c)
+  {
+    switch (c)
+    {
+      case 'A':
+        return 1;
+      case 'B':
+        return 10;
+      case 'C':
+        return 100;
+      case 'D':
+        return 1000;
+    }
+    std::cout << "Invalid char: " << c << std::endl;
+    return 0;
+  }
+
+  std::vector<std::pair<int, State>> ValidStates(int height, const State& state)
+  {
+    std::vector<std::pair<int, State>> newStates;
+    for (auto& piece : state)
+    {
+      if (piece.first.y > 0)
+      {  // Piece is in the room, move to hallway
+
+        // Check if already at correct position
+        bool canMove = false;
+        if (piece.first.x == (piece.second - 'A') * 2 + 2)
+        {
+          for (int i = piece.first.y + 1; i < 1 + height; i++)
+          {
+            if (state.find({piece.first.x, i})->second != piece.second)
+            {
+              canMove = true;
+              break;
+            }
+          }
+        }
+        else
+          canMove = true;
+
+        // Check if piece is obstructed by others in the room
+        for (int i = piece.first.y - 1; i > 0; i--)
+        {
+          if (state.count({piece.first.x, i}) != 0)
+          {
+            canMove = false;
+            break;
+          }
+        }
+
+        if (canMove)
+        {
+          // Check hallways to the left
+          for (int i = piece.first.x - 1; i >= 0; i--)
+          {
+            // Is valid position in hallway
+            if (i == 0 || i % 2 == 1 || i == 10)
+            {
+              if (state.count({i, 0}) == 0)
+              {
+                State newState = state;
+                newState[{i, 0}] = piece.second;
+                newState.erase(piece.first);
+                newStates.emplace_back(std::pair<int, State>{
+                  (piece.first.y + std::abs(piece.first.x - i)) * GetCost(piece.second), newState});
+              }
+              else
+                break;
+            }
+          }
+
+          // Check hallways to the right
+          for (int i = piece.first.x + 1; i < 11; i++)
+          {
+            // Is valid position in hallway
+            if (i == 0 || i % 2 == 1 || i == 10)
+            {
+              if (state.count({i, 0}) == 0)
+              {
+                State newState = state;
+                newState[{i, 0}] = piece.second;
+                newState.erase(piece.first);
+                newStates.emplace_back(std::pair<int, State>{
+                  (piece.first.y + std::abs(piece.first.x - i)) * GetCost(piece.second), newState});
+              }
+              else
+                break;
+            }
+          }
+        }
+      }
+      else
+      {  // Piece is in the hallway, move to room
+
+        int x = (piece.second - 'A') * 2 + 2;
+        int dir = Helper::Sign(x - piece.first.x);
+        bool canMove = true;
+
+        // Check if hallway is clear to correct position
+        for (int i = piece.first.x + dir; (dir < 0 && i > x) || (dir > 0 && i < x); i += dir)
+        {
+          if (state.count({i, 0}) != 0)
+          {
+            canMove = false;
+            break;
+          }
+        }
+
+        if (canMove)
+        {
+          // Check if room is filled with same piece or no pieces
+          int pos = height;
+          for (int i = 1; i < 1 + height; i++)
+          {
+            if (state.count({x, i}) != 0)
+            {
+              if (state.find({x, i})->second == piece.second)
+              {
+                if (pos == height)
+                  pos = i - 1;
+              }
+              else
+              {
+                pos = 0;
+                break;
+              }
+            }
+          }
+          if (pos != 0)
+          {
+            State newState = state;
+            newState[{x, pos}] = piece.second;
+            newState.erase(piece.first);
+            newStates.emplace_back(
+              std::pair<int, State>{(pos + std::abs(piece.first.x - x)) * GetCost(piece.second), newState});
+          }
+        }
+      }
+    }
+    return newStates;
+  }
+
+  int Solve(const State& state, int h)
+  {
+    return Helper::AStar(h, state, Heuristic, ValidStates, ValidateState);
+  }
+
+  REGISTER_DAY(2021, Day23, State, int);
+
+  REGISTER_TEST_EXAMPLE(2021, Day23, ExampleInput, 1, 12521);
+  REGISTER_TEST(2021, Day23, Input, 1, 14350);
+  REGISTER_TEST_EXAMPLE(2021, Day23, ExampleInput, 2, 44169);
+  REGISTER_TEST(2021, Day23, Input, 2, 49742);
+
+  READ_INPUT(input)
+  {
+    std::string str;
+    getline(input, str);
+    getline(input, str);
+    getline(input, str);
+    std::map<Index2D, char> state;
+    state.emplace(Index2D{2, 1}, str[3]);
+    state.emplace(Index2D{4, 1}, str[5]);
+    state.emplace(Index2D{6, 1}, str[7]);
+    state.emplace(Index2D{8, 1}, str[9]);
+
+    getline(input, str);
+    state.emplace(Index2D{2, 2}, str[3]);
+    state.emplace(Index2D{4, 2}, str[5]);
+    state.emplace(Index2D{6, 2}, str[7]);
+    state.emplace(Index2D{8, 2}, str[9]);
+
+    return state;
+  }
+
+  OUTPUT1(input)
+  {
+    return Solve(input, 2);
+  }
+
+  OUTPUT2(input)
+  {
+    State state;
+    for (auto& piece : input)
+    {
+      if (piece.first.y == 2)
+        state.emplace(Index2D{piece.first.x, 4}, piece.second);
+      else
+        state.emplace(piece.first, piece.second);
+    }
+    state.emplace(Index2D{2, 2}, 'D');
+    state.emplace(Index2D{2, 3}, 'D');
+    state.emplace(Index2D{4, 2}, 'C');
+    state.emplace(Index2D{4, 3}, 'B');
+    state.emplace(Index2D{6, 2}, 'B');
+    state.emplace(Index2D{6, 3}, 'A');
+    state.emplace(Index2D{8, 2}, 'A');
+    state.emplace(Index2D{8, 3}, 'C');
+
+    return Solve(state, 4);
+  }
+}
diff --git a/src/2021/Day24.cpp b/src/2021/Day24.cpp
new file mode 100644
index 0000000..0735112
--- /dev/null
+++ b/src/2021/Day24.cpp
@@ -0,0 +1,126 @@
+#include "common/aoc.h"
+
+namespace y2021::day24
+{
+
+  enum class Operation
+  {
+    Inp,
+    Add,
+    Mul,
+    Div,
+    Mod,
+    Eql
+  };
+
+  struct Instruction
+  {
+    Operation operation;
+    char dst;
+    std::string src;
+  };
+
+  int64_t Read(const std::string& str, const std::map<char, int64_t>& data)
+  {
+    if (str[0] >= 'a' && str[0] <= 'z')
+    {
+      auto it = data.find(str[0]);
+      if (it != data.end())
+        return it->second;
+      return 0;
+    }
+    return atoll(str.c_str());
+  };
+
+  int64_t Read(char c, const std::map<char, int64_t>& data)
+  {
+    auto it = data.find(c);
+    if (it != data.end())
+      return it->second;
+    return 0;
+  }
+
+  bool ValidateInput(const std::vector<Instruction>& instructions, const std::string& str)
+  {
+    int inputOffset = 0;
+    std::map<char, int64_t> data;
+    for (int i = 0; i < instructions.size(); i++)
+    {
+      switch (instructions[i].operation)
+      {
+        case Operation::Inp:
+          data[instructions[i].dst] = str[inputOffset++] - '0';
+          break;
+        case Operation::Add:
+          data[instructions[i].dst] = Read(instructions[i].dst, data) + Read(instructions[i].src, data);
+          break;
+        case Operation::Mul:
+          data[instructions[i].dst] = Read(instructions[i].dst, data) * Read(instructions[i].src, data);
+          break;
+        case Operation::Div:
+          data[instructions[i].dst] = Read(instructions[i].dst, data) / Read(instructions[i].src, data);
+          break;
+        case Operation::Mod:
+          data[instructions[i].dst] = Read(instructions[i].dst, data) % Read(instructions[i].src, data);
+          break;
+        case Operation::Eql:
+          data[instructions[i].dst] = Read(instructions[i].dst, data) == Read(instructions[i].src, data) ? 1 : 0;
+          break;
+        default:
+          std::cout << "Invalid operation" << std::endl;
+      }
+    }
+    return data['z'] == 0;
+  }
+
+  REGISTER_DAY(2021, Day24, std::vector<Instruction>, int64_t);
+
+  REGISTER_TEST(2021, Day24, Input, 1, 99919765949498);
+  REGISTER_TEST(2021, Day24, Input, 2, 24913111616151);
+
+  READ_INPUT(input)
+  {
+    std::vector<Instruction> instructions;
+    std::string str;
+    while (getline(input, str))
+    {
+      Instruction instruction;
+      std::string_view sv(str.c_str(), 3);
+      if (sv == "inp")
+        instruction.operation = Operation::Inp;
+      else if (sv == "add")
+        instruction.operation = Operation::Add;
+      else if (sv == "mul")
+        instruction.operation = Operation::Mul;
+      else if (sv == "div")
+        instruction.operation = Operation::Div;
+      else if (sv == "mod")
+        instruction.operation = Operation::Mod;
+      else if (sv == "eql")
+        instruction.operation = Operation::Eql;
+      else
+        std::cout << "Invalid operation: " << sv << std::endl;
+      instruction.dst = str[4];
+      if (instruction.operation != Operation::Inp)
+        instruction.src = str.substr(6);
+      instructions.emplace_back(instruction);
+    }
+    return instructions;
+  }
+
+  OUTPUT1(input)
+  {
+    std::string str = "99919765949498";
+    if (ValidateInput(input, str))
+      return atoll(str.c_str());
+    return 0;
+  }
+
+  OUTPUT2(input)
+  {
+    std::string str = "24913111616151";
+    if (ValidateInput(input, str))
+      return atoll(str.c_str());
+    return 0;
+  }
+}
diff --git a/src/2021/Day25.cpp b/src/2021/Day25.cpp
new file mode 100644
index 0000000..1f09f58
--- /dev/null
+++ b/src/2021/Day25.cpp
@@ -0,0 +1,66 @@
+#include "common/aoc.h"
+
+namespace y2021::day25
+{
+  REGISTER_DAY(2021, Day25, Array2D<char>, int);
+
+  REGISTER_TEST_EXAMPLE(2021, Day25, ExampleInput, 1, 58);
+  REGISTER_TEST(2021, Day25, Input, 1, 419);
+
+  READ_INPUT(input)
+  {
+    return Input::ReadArray2D(input);
+  }
+
+  OUTPUT1(inputConst)
+  {
+    Array2D<char> input = inputConst;
+    bool hasMoved = true;
+    int i = 0;
+    while (hasMoved)
+    {
+      hasMoved = false;
+      Array2D<char> cpy = input;
+      Index2D index{0, 0};
+      for (auto& c : cpy)
+      {
+        if (c == '>')
+        {
+          Index2D newIndex = index;
+          newIndex.x = (newIndex.x + 1) % cpy.width;
+          if (cpy[newIndex] == '.')
+          {
+            input[newIndex] = '>';
+            input[index] = '.';
+            hasMoved = true;
+          }
+        }
+        cpy.Increment(index);
+      }
+      cpy = input;
+      index = {0, 0};
+      for (auto& c : cpy)
+      {
+        if (c == 'v')
+        {
+          Index2D newIndex = index;
+          newIndex.y = (newIndex.y + 1) % cpy.height;
+          if (cpy[newIndex] == '.')
+          {
+            input[newIndex] = 'v';
+            input[index] = '.';
+            hasMoved = true;
+          }
+        }
+        cpy.Increment(index);
+      }
+      i++;
+    }
+    return i;
+  }
+
+  OUTPUT2(input)
+  {
+    return 0;
+  }
+}