#include "aoc.h"
#include <deque>
#include <set>

namespace aoc2016 {

struct pos {
  int64_t x;
  int64_t y;
  int64_t n;

  friend bool operator<(pos p1, pos p2) { return p1.x < p2.x ? true : p1.x > p2.x ? false : p1.y < p2.y; }
  bool operator==(pos p) const noexcept { return x == p.x && y == p.y; }
};

bool is_space(int64_t x, int64_t y, int64_t favorite) {
  int64_t a = x * x + 3 * x + 2 * x * y + y + y * y + favorite;
  int64_t c = __builtin_popcount(a);
  return x >= 0 && y >= 0 && (c & 1) == 0;
}

int64_t bfs(pos start, pos end, int64_t favorite, std::set<pos>& visited) {
  std::deque<pos> q;

  q.push_back(start);
  visited.insert(start);

  while (!q.empty()) {
    auto s = q.size();
    while (s-- > 0) {
      auto p0 = q.front();
      q.pop_front();
      visited.insert(p0);

      if (p0 == end) {
        return p0.n;
      } else {
        pos ns[4] = {
            {p0.x - 1, p0.y, p0.n + 1},
            {p0.x + 1, p0.y, p0.n + 1},
            {p0.x, p0.y - 1, p0.n + 1},
            {p0.x, p0.y + 1, p0.n + 1},
        };
        for (pos p : ns) {
          if (is_space(p.x, p.y, favorite)) {
            auto it = visited.find(p);
            if (it == visited.end() || it->n > p.n) {
              q.push_back(p);
            }
          }
        }
      }
    }
  }
  return INT64_MAX;
}

std::pair<int64_t, int64_t> day13(line_view) {
  std::set<pos> visited;
  int64_t s = bfs({1, 1, 0}, {31, 39, INT64_MAX}, 1352, visited);
  int64_t total{0};
  for (auto& p : visited) {
    if (p.n <= 50) {
      total += 1;
    }
  }
  return {s, total};
}
} // namespace aoc2016