aocpp/day15.cpp

#include <iterator>
#include <iostream>
#include <utility>
#include <tuple>
#include <map>
#include <deque>
#include <vector>

#include <intcode/intcode.hpp>
using namespace intcode;

namespace {

using Coord = std::pair<ValueType, ValueType>;

auto Compute(Machine machine) -> std::pair<int,int> {
  Coord here {0,0};
  std::map<Coord, ValueType> world {{{0,0},1}};

  using State = std::tuple<Coord, Machine>;

  std::vector<State> layer {{{0,0}, std::move(machine)}};
  std::vector<State> next_layer;
  
  auto action = [&](Machine m, ValueType cmd, Coord coord) {
    if (!world.contains(coord)) {
      std::get<Input>(Step(m)).pos = cmd;
      auto o = std::get<Output>(Step(m)).val;
      world[coord] = o;
      if (o) {
        next_layer.emplace_back(coord, std::move(m));
      }
    }
  };

  int part1 = 0;
  while (!layer.empty()) {
    for (auto && s : layer) {
      auto& [loc, m] = s;
      if (2 == world[loc]) {
        world.clear();
        world[loc] = 2;
        auto start = std::move(m);
        layer.clear();
        layer.push_back({loc, std::move(start)});
        goto loop2;
      }
      auto [x,y] = loc;
      action(m, 1, {x,y-1});
      action(m, 2, {x,y+1});
      action(m, 3, {x-1,y});
      action(std::move(m), 4, {x+1,y});
    }
    layer = std::move(next_layer);
    next_layer.clear();
    part1++;
  }

  
loop2:
  int part2 = 0;
  while (!layer.empty()) {
    for (auto && s : layer) {
      auto& [loc, m] = s;
      auto [x,y] = loc;
      action(m, 1, {x,y-1});
      action(m, 2, {x,y+1});
      action(m, 3, {x-1,y});
      action(std::move(m), 4, {x+1,y});
    }
    layer = std::move(next_layer);
    next_layer.clear();
    part2++;
  }
  return {part1, part2-1};
}

} // namespace

auto main() -> int {
  auto machine = Machine{ParseStream(std::cin)};
  auto [part1, part2] = Compute(machine);
  std::cout << "Part 1: " << part1 << std::endl;
  std::cout << "Part 2: " << part2 << std::endl;
}