From 7b2567a71eaa729f6b604589f3f794fff7014e0d Mon Sep 17 00:00:00 2001
From: Thraix <thraix@hotmail.com>
Date: Thu, 27 Aug 2026 21:41:22 +0200
Subject: [PATCH] Add solution for 2016 Day 16

---
 res/2016/day16/test_input.txt |  1 +
 src/2016/Day16.cpp            | 47 +++++++++++++++++++++++++++--------
 2 files changed, 38 insertions(+), 10 deletions(-)

diff --git a/res/2016/day16/test_input.txt b/res/2016/day16/test_input.txt
index e69de29..5caff40 100644
--- a/res/2016/day16/test_input.txt
+++ b/res/2016/day16/test_input.txt
@@ -0,0 +1 @@
+10000
diff --git a/src/2016/Day16.cpp b/src/2016/Day16.cpp
index d957b41..07b589e 100644
--- a/src/2016/Day16.cpp
+++ b/src/2016/Day16.cpp
@@ -2,30 +2,57 @@
 
 namespace y2016::day16
 {
-  REGISTER_DAY(2016, Day16, std::vector<int>, int);
+  REGISTER_DAY(2016, Day16, std::string, std::string);
 
-  REGISTER_TEST_EXAMPLE(2016, Day16, ExampleInput, 1, 0);
-  REGISTER_TEST(2016, Day16, Input, 1, 0);
-  REGISTER_TEST_EXAMPLE(2016, Day16, ExampleInput, 2, 0);
-  REGISTER_TEST(2016, Day16, Input, 2, 0);
+  REGISTER_TEST_EXAMPLE(2016, Day16, ExampleInput, 1, "01100");
+  REGISTER_TEST(2016, Day16, Input, 1, "10100011010101011");
+  REGISTER_TEST(2016, Day16, Input, 2, "01010001101011001");
 
   READ_INPUT(input)
   {
-    std::vector<int> vec;
     std::string str;
-    while (getline(input, str))
+    getline(input, str);
+    return str;
+  }
+
+  std::string ReverseFlip(const std::string& str)
+  {
+    std::string reverse;
+    for (int i = str.size() - 1; i >= 0; i--)
     {
+      reverse.push_back(str[i] == '1' ? '0' : '1');
     }
-    return vec;
+    return reverse;
+  }
+
+  std::string Solve(std::string str, int length)
+  {
+    while (str.size() < length)
+    {
+      str = str + "0" + ReverseFlip(str);
+    }
+    str = str.substr(0, length);
+
+    std::string checksum;
+    while (str.size() % 2 == 0)
+    {
+      for (int i = 0; i < str.size(); i += 2)
+      {
+        checksum.push_back(str[i] == str[i + 1] ? '1' : '0');
+      }
+      str = checksum;
+      checksum.clear();
+    }
+    return str;
   }
 
   OUTPUT1(input)
   {
-    return 0;
+    return Solve(input, isExample ? 20 : 272);
   }
 
   OUTPUT2(input)
   {
-    return 0;
+    return Solve(input, 35651584);
   }
 }