From cdf00cb66aef4fad57f3d1356c5c9feb9821b361 Mon Sep 17 00:00:00 2001
From: Thraix <thraix@hotmail.com>
Date: Sun, 30 Aug 2026 22:50:54 +0200
Subject: [PATCH] Add solution for 2016 Day 16

- Fix Md5 algorithm
---
 res/2016/day17/test_input.txt |  1 +
 src/2016/Day17.cpp            | 76 ++++++++++++++++++++++++++++++-----
 src/common/lib/Md5.cpp        | 32 ++++++++++++++-
 3 files changed, 97 insertions(+), 12 deletions(-)

diff --git a/res/2016/day17/test_input.txt b/res/2016/day17/test_input.txt
index e69de29..d1f0ba9 100644
--- a/res/2016/day17/test_input.txt
+++ b/res/2016/day17/test_input.txt
@@ -0,0 +1 @@
+ulqzkmiv
diff --git a/src/2016/Day17.cpp b/src/2016/Day17.cpp
index ed2fa22..2ea9f98 100644
--- a/src/2016/Day17.cpp
+++ b/src/2016/Day17.cpp
@@ -2,30 +2,84 @@
 
 namespace y2016::day17
 {
-  REGISTER_DAY(2016, Day17, std::vector<int>, int);
+  REGISTER_DAY(2016, Day17, std::string, std::string);
 
-  REGISTER_TEST_EXAMPLE(2016, Day17, ExampleInput, 1, 0);
-  REGISTER_TEST(2016, Day17, Input, 1, 0);
-  REGISTER_TEST_EXAMPLE(2016, Day17, ExampleInput, 2, 0);
-  REGISTER_TEST(2016, Day17, Input, 2, 0);
+  REGISTER_TEST_EXAMPLE(2016, Day17, ExampleInput, 1, "DRURDRUDDLLDLUURRDULRLDUUDDDRR");
+  REGISTER_TEST(2016, Day17, Input, 1, "DUDDRLRRRD");
+  REGISTER_TEST_EXAMPLE(2016, Day17, ExampleInput, 2, "830");
+  REGISTER_TEST(2016, Day17, Input, 2, "578");
 
   READ_INPUT(input)
   {
     std::vector<int> vec;
     std::string str;
-    while (getline(input, str))
-    {
-    }
-    return vec;
+    getline(input, str);
+    return str;
+  }
+
+  struct State
+  {
+    std::string str{""};
+    int x{0};
+    int y{0};
+  };
+
+  bool IsOpen(char c)
+  {
+    return c >= 'b' && c <= 'f';
+  }
+
+  void Branch(const State& state, std::queue<State>& queue)
+  {
+    std::string hash = Md5::Hash(state.str);
+    if (state.y > 0 && IsOpen(hash[0]))
+      queue.emplace(State{state.str + "U", state.x, state.y - 1});
+    if (state.y < 3 && IsOpen(hash[1]))
+      queue.emplace(State{state.str + "D", state.x, state.y + 1});
+    if (state.x > 0 && IsOpen(hash[2]))
+      queue.emplace(State{state.str + "L", state.x - 1, state.y});
+    if (state.x < 3 && IsOpen(hash[3]))
+      queue.emplace(State{state.str + "R", state.x + 1, state.y});
+  }
+
+  bool IsGoal(const State& state)
+  {
+    return state.x == 3 && state.y == 3;
   }
 
   OUTPUT1(input)
   {
-    return 0;
+    std::queue<State> queue;
+    queue.emplace(State{input, 0, 0});
+    while (!queue.empty())
+    {
+      State state = queue.front();
+      queue.pop();
+      if (IsGoal(state))
+        return state.str.substr(input.size());
+      Branch(state, queue);
+    }
+
+    return "";
   }
 
   OUTPUT2(input)
   {
-    return 0;
+    std::queue<State> queue;
+    queue.emplace(State{input, 0, 0});
+    int longest = 0;
+    while (!queue.empty())
+    {
+      State state = queue.front();
+      queue.pop();
+      if (IsGoal(state))
+      {
+        longest = state.str.size() - input.size();
+        continue;
+      }
+      Branch(state, queue);
+    }
+
+    return std::to_string(longest);
   }
 }
diff --git a/src/common/lib/Md5.cpp b/src/common/lib/Md5.cpp
index de8218a..2db3908 100644
--- a/src/common/lib/Md5.cpp
+++ b/src/common/lib/Md5.cpp
@@ -5,6 +5,30 @@
 #include <iomanip>
 #include <iostream>
 
+#undef AOC_MD5_TESTING
+
+void PrintData(uint8_t* data)
+{
+  for (int i = 0; i < 8; i++)
+  {
+    for (int j = 0; j < 8; j++)
+    {
+      std::cout << std::hex << std::setw(2) << std::setfill('0') << (int)data[i * 8 + j];
+    }
+    std::cout << " ";
+    for (int j = 0; j < 8; j++)
+    {
+      if (data[i * 8 + j] >= 32 && data[i * 8 + j] < 126)
+        std::cout << data[i * 8 + j];
+      else
+        std::cout << "?";
+    }
+    std::cout << std::endl;
+  }
+
+  std::cout << std::dec << std::endl;
+}
+
 uint32_t Md5::BytesToUint32(uint8_t* data)
 {
   return ((uint32_t)data[3] << 24) | ((uint32_t)data[2] << 16) | ((uint32_t)data[1] << 8) | (uint32_t)data[0];
@@ -17,6 +41,9 @@ uint32_t Md5::LeftRotate(uint32_t x, uint32_t n)
 
 void Md5::Transform(uint8_t* data, uint32_t& a0, uint32_t& b0, uint32_t& c0, uint32_t& d0)
 {
+#ifdef AOC_MD5_TESTING
+  PrintData(data);
+#endif
   // clang-format off
   const static std::array<uint32_t, 64> K
   {
@@ -116,7 +143,10 @@ std::string Md5::Hash(std::string str)
   uint64_t offset = 0;
   for (int i = 0; i < loops - 1; i++)
   {
-    Transform((uint8_t*)(str.c_str() + offset), a0, b0, c0, d0);
+    uint8_t data[64];
+    std::memset(data, 0x0, 64);
+    std::memcpy(data, str.c_str() + offset, std::min<int>(str.size() - offset, 64));
+    Transform(data, a0, b0, c0, d0);
     offset += 64;
   }