aocpp/day15.cpp

#include <deque>
#include <iostream>
#include <set>
#include <tuple>
#include <utility>

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

namespace {

std::pair<ValueType, Coord(*)(Coord)> const moves[4]
  {{1, Up}, {2, Down}, {3, Left}, {4, Right}};

auto Fork(Machine m, ValueType cmd) {
  std::get<Input>(Step(m)).pos = cmd;
  auto o = std::get<Output>(Step(m)).val;
  return std::make_pair(o, std::move(m));
}

auto Compute(Machine machine) {
  Coord const origin {0,0};
  std::set<Coord> world {origin};

  std::deque<std::tuple<int, Coord, Machine>> todo
    {{0, origin, std::move(machine)}};

  long part1 = -1;
  long part2 = -1;

top:
  while (!todo.empty()) {
    auto & [steps, loc, m] = todo.front();
    part2 = steps;
    steps++;

    for (auto&& [cmd, fun] : moves) {
      auto loc_ = fun(loc);
      if (world.insert(loc_).second) {
        auto [o,m_] = Fork(m, cmd);
        switch (o) {
          case 2:
            part1 = steps;
            world = {origin};
            todo = {{0, origin, std::move(m_)}};
            goto top;
          case 1:
            todo.emplace_back(steps, loc_, std::move(m_));
        }
      }
    }
    todo.pop_front();
  }

  return std::make_pair(part1,part2);
}

} // namespace

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