Add day11 in C++

day11.h

@@ -0,0 +1,141 @@
+#include <fstream>
+#include <map>
+#include <optional>
+#include <unordered_map>
+
+namespace {
+  using namespace std;
+
+  using State = tuple<int, int, unordered_map<int, long long>>;
+  using Panels = map<pair<int, int>, int>;
+
+  enum class Direction {
+    Up, Right, Down, Left
+  };
+
+  Direction turn(Direction facing, int direction) {
+    if (direction == 0) {
+      switch (facing) {
+      case Direction::Up:
+        return Direction::Left;
+      case Direction::Right:
+        return Direction::Up;
+      case Direction::Down:
+        return Direction::Right;
+      case Direction::Left:
+        return Direction::Down;
+      }
+    }
+    if (direction == 1) {
+      switch (facing) {
+      case Direction::Up:
+        return Direction::Right;
+      case Direction::Right:
+        return Direction::Down;
+      case Direction::Down:
+        return Direction::Left;
+      case Direction::Left:
+        return Direction::Up;
+      }
+    }
+  }
+
+  pair<int, int> move(pair<int, int> pos, Direction facing) {
+    auto [x, y] = pos;
+    switch (facing) {
+    case Direction::Up:
+      return { x, y + 1 };
+    case Direction::Right:
+      return { x + 1, y };
+    case Direction::Down:
+      return { x, y - 1 };
+    case Direction::Left:
+      return { x - 1, y };
+    }
+  }
+
+  unordered_map<int, long long> parse(ifstream input) {
+    unordered_map<int, long long> program;
+    long long value;
+    for (int pos = 0; input >> value; pos++) {
+      program[pos] = value;
+      input.ignore(1, ',');
+    }
+    return program;
+  }
+
+  optional<int> run(State& state, optional<int> input) {
+    auto& [pos, base, program] = state;
+    while (program[pos] != 99) {
+      int op = program[pos] % 100;
+      auto param = [&, mode = program[pos++] / 10]() mutable -> long long& {
+        mode /= 10;
+        switch (mode % 10) {
+        case 0:
+          return program[program[pos++]];
+        case 1:
+          return program[pos++];
+        case 2:
+          return program[base + program[pos++]];
+        }
+      };
+      if (op == 1) {
+        param() = param() + param();
+      } else if (op == 2) {
+        param() = param() * param();
+      } else if (op == 3) {
+        param() = *input;
+      } else if (op == 4) {
+        return param();
+      } else if (op == 5) {
+        pos = param() != 0 ? param() : pos + 1;
+      } else if (op == 6) {
+        pos = param() == 0 ? param() : pos + 1;
+      } else if (op == 7) {
+        auto left = param();
+        param() = left < param() ? 1 : 0;
+      } else if (op == 8) {
+        param() = param() == param() ? 1 : 0;
+      } else if (op == 9) {
+        base += param();
+      }
+    }
+    return {};
+  }
+
+  void paint(unordered_map<int, long long> program, Panels& panels) {
+    State state{ 0, 0, move(program) };
+    pair<int, int> pos;
+    auto facing = Direction::Up;
+    while (auto color = run(state, panels[pos])) {
+      auto direction = run(state, {});
+      panels[pos] = *color;
+      facing = turn(facing, *direction);
+      pos = move(pos, facing);
+    }
+  }
+
+  string draw(const Panels& panels) {
+    string id;
+    int line = 0;
+    for (auto&& [panel, color] : panels) {
+      if (panel.first != line)
+        id += '\n';
+      id += ".#"[color];
+      line = panel.first;
+    }
+    return id;
+  }
+
+  auto part1(ifstream input) {
+    Panels panels;
+    paint(parse(move(input)), panels);
+    return panels.size();
+  }
+
+  string part2(ifstream input) {
+    Panels panels{ { {0, 0}, 1 } };
+    paint(parse(move(input)), panels);
+    return draw(panels);
+  }
+}