Add solution for 2016 Day 17

- Fix Md5 algorithm

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);
   }
 }