Attempt solving day 15 part 2

Author: fwcd

Diff for: day15/resources/double.txt

@@ -0,0 +1,9 @@
+#######
+#...#.#
+#.....#
+#..OO@#
+#..O..#
+#.....#
+#######
+
+<vv<<^^<<^^

Diff for: day15/src/day15.cpp

@@ -14,16 +14,30 @@ struct Vec2 {
   Vec2<T> operator+(const Vec2<T> &rhs) const {
     return {x + rhs.x, y + rhs.y};
   }
+
+  Vec2<T> operator-(const Vec2<T> &rhs) const {
+    return {x - rhs.x, y - rhs.y};
+  }
+
+  void operator+=(const Vec2<T> &rhs) {
+    x += rhs.x;
+    y += rhs.y;
+  }
+
+  void operator-=(const Vec2<T> &rhs) {
+    x -= rhs.x;
+    y -= rhs.y;
+  }
 };
 
-enum class Inst : char {
+enum class Dir : char {
   Left = '<',
   Up = '^',
   Right = '>',
   Down = 'v',
 };
 
-std::ostream &operator<<(std::ostream &os, Inst inst) {
+std::ostream &operator<<(std::ostream &os, Dir inst) {
   os << char(inst);
   return os;
 }
@@ -53,26 +67,48 @@ struct Board {
     return rows[pos.y][pos.x];
   }
 
-  void perform(Inst inst) {
+  bool is_box(Vec2<int> pos, bool include_end = true) const {
+    char cell = (*this)[pos];
+    return cell == 'O' || cell == '[' || (include_end && cell == ']');
+  }
+
+  bool is_space(Vec2<int> pos) const {
+    return (*this)[pos] == '.';
+  }
+
+  bool is_wall(Vec2<int> pos) const {
+    return (*this)[pos] == '#';
+  }
+
+  void perform(Dir inst) {
     Vec2<int> dir;
     switch (inst) {
-    case Inst::Left: dir = {-1, 0}; break;
-    case Inst::Up: dir = {0, -1}; break;
-    case Inst::Right: dir = {1, 0}; break;
-    case Inst::Down: dir = {0, 1}; break;
+    case Dir::Left: dir = {-1, 0}; break;
+    case Dir::Up: dir = {0, -1}; break;
+    case Dir::Right: dir = {1, 0}; break;
+    case Dir::Down: dir = {0, 1}; break;
     }
 
     Vec2<int> next = robot + dir;
     Vec2<int> end = next;
-    while ((*this)[end] == 'O') {
-      end = end + dir;
+    while (is_box(end)) {
+      end += dir;
     }
 
-    if ((*this)[end] != '#') {
-      robot = next;
-      if ((*this)[next] == 'O' && (*this)[end] == '.') {
-        std::swap((*this)[next], (*this)[end]);
+    if (!is_wall(end)) {
+      if (is_box(next) && is_space(end)) {
+        for (Vec2<int> pos = end; pos != robot; pos -= dir) {
+          Vec2<int> prev = pos - dir;
+          (*this)[pos] = (*this)[prev];
+
+          Vec2<int> offset = {1, 0};
+          switch ((*this)[pos]) {
+          case '[': std::swap((*this)[pos + offset], (*this)[prev + offset]); break;
+          case ']': std::swap((*this)[pos - offset], (*this)[prev - offset]); break;
+          }
+        }
       }
+      robot = next;
     }
   }
 
@@ -81,8 +117,7 @@ struct Board {
 
     for (int y = 0; y < height(); y++) {
       for (int x = 0; x < width(); x++) {
-        char cell = (*this)[{x, y}];
-        if (cell == 'O' || cell == '[') {
+        if (is_box({x, y}, /*include_end=*/false)) {
           sum += 100 * y + x;
         }
       }
@@ -109,7 +144,7 @@ std::ostream &operator<<(std::ostream &os, const Board &board) {
 struct State {
   Board board1;
   Board board2;
-  std::vector<Inst> insts;
+  std::vector<Dir> insts;
 
   static State parse_from(std::istream &istream) {
     State state;
@@ -147,7 +182,7 @@ struct State {
         }
       } else {
         for (char raw_inst : line) {
-          state.insts.push_back(Inst(raw_inst));
+          state.insts.push_back(Dir(raw_inst));
         }
       }
     }
@@ -156,7 +191,7 @@ struct State {
   }
 
   void run() {
-    for (Inst inst : insts) {
+    for (Dir inst : insts) {
       board1.perform(inst);
       board2.perform(inst);
     }
@@ -179,9 +214,13 @@ int main(int argc, char *argv[]) {
 
   std::cout << state.board1;
   std::cout << state.board2;
-  state.run();
-  std::cout << "Part 1: " << state.board1.sum_box_coords() << std::endl;
-  std::cout << "Part 2: " << state.board2.sum_box_coords() << std::endl;
+  for (Dir inst : state.insts) {
+    state.board2.perform(inst);
+    std::cout << "After " << inst << ": " << std::endl << state.board2;
+  }
+  // state.run();
+  // std::cout << "Part 1: " << state.board1.sum_box_coords() << std::endl;
+  // std::cout << "Part 2: " << state.board2.sum_box_coords() << std::endl;
 
   return 0;
 }