Initial commit with solutions from 2024

src/2024/Day20.cpp

@@ -0,0 +1,93 @@
+#include "common/aoc.h"
+
+namespace day20
+{
+  REGISTER_DAY(2024, Day20, Array2D<char>, int32_t);
+
+  REGISTER_TEST_EXAMPLE(2024, Day20, ExampleInput, 1, 1);
+  REGISTER_TEST(2024, Day20, Input, 1, 1429);
+  REGISTER_TEST_EXAMPLE(2024, Day20, ExampleInput, 2, 285);
+  REGISTER_TEST(2024, Day20, Input, 2, 988931);
+
+  READ_INPUT(input)
+  {
+    return Input::ReadArray2D(input);
+  }
+
+  // Single path DFS, assumes the path can never hit a dead end
+  static std::pair<int, std::vector<Index2D>> DFS(const Array2D<char>& map, const Index2D& initial)
+  {
+    std::vector<Index2D> path;
+    Index2D prev = Index2D{-1, -1};
+    std::pair<int, Index2D> cur{0, initial};
+    path.emplace_back(initial);
+
+    while (map[cur.second] != 'E')
+    {
+      for (auto dir : Helper::GetNeighborDirections())
+      {
+        Index2D pos = cur.second + dir;
+        if (map.IsInside(pos))
+        {
+          if (pos != prev && map[pos] != '#')
+          {
+            prev = cur.second;
+            cur.first++;
+            cur.second = pos;
+            path.emplace_back(pos);
+            break;
+          }
+        }
+      }
+    }
+    return {cur.first, path};
+  }
+
+  int Cheat(const Array2D<char>& map, int cheatTime, int diff)
+  {
+    int sum = 0;
+    std::pair<int, std::vector<Index2D>> path = DFS(map, map.Find('S'));
+
+    std::vector<int> distanceToGoal(map.width * map.height, -1);
+    for (int i = 0; i < path.second.size(); i++)
+    {
+      distanceToGoal[map.GetIndex(path.second[i])] = path.second.size() - i - 1;
+    }
+
+    for (int i = 0; i < path.second.size(); i++)
+    {
+      for (int y = -cheatTime; y <= cheatTime; y++)
+      {
+        int yAbs = std::abs(y);
+        for (int x = -cheatTime + yAbs; x <= cheatTime - yAbs; x++)
+        {
+          int xAbs = std::abs(x);
+          int cost = i + xAbs + yAbs;
+          Index2D pos{path.second[i].x + x, path.second[i].y + y};
+          if (map.IsInside(pos))
+          {
+            int index = map.GetIndex(pos);
+            if (distanceToGoal[index] >= 0)
+            {
+              if (cost + distanceToGoal[index] <= path.first - diff)
+              {
+                sum++;
+              }
+            }
+          }
+        }
+      }
+    }
+    return sum;
+  }
+
+  OUTPUT1(input)
+  {
+    return Cheat(input, 2, isExample ? 50 : 100);
+  }
+
+  OUTPUT2(input)
+  {
+    return Cheat(input, 20, isExample ? 50 : 100);
+  }
+}