aocpp/day23.cpp

#include <cstddef>
#include <deque>
#include <iostream>
#include <stdexcept>
#include <tuple>
#include <utility>
#include <variant>
#include <vector>

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

namespace {

using Packet = std::pair<ValueType, ValueType>;
using Ethernet = std::deque<std::pair<std::size_t, Packet>>;

auto BuildNetwork(Machine m) -> std::vector<Machine> {
  std::vector<Machine> machines;
  for (int i = 0; i < 50; i++) {
    machines.push_back(m);
    StepInput(machines.back(), i);
  }
  return machines;
}

auto Interact(Ethernet & ethernet, Machine & m, std::optional<Packet> p) -> void {
  while(std::visit(overloaded{

  [&](Input i) {
    if (p) {
      i.pos = p->first;
      StepInput(m, p->second);
      p = {};
      return true;
    }
    i.pos = -1; // no packet
    return false;
  },

  [&](Output o) {
    auto x = StepOutput(m);
    auto y = StepOutput(m);
    ethernet.push_back({o.val, {x,y}});
    return true;
  },

  [](Halt) -> bool { throw std::runtime_error{"unexpected halt"}; },
  }, Step(m))) {}
}

} // namespace

auto main() -> int {
  auto machines = BuildNetwork(Machine{ParseStream(std::cin)});
  auto ethernet = Ethernet{};

  std::optional<ValueType> part1;
  std::optional<ValueType> part2;
  std::optional<Packet> nat;

  for(;;) {
    if (ethernet.empty()) {
      if (nat) {
        if (nat->second == part2) { break; }
        part2 = nat->second;
        Interact(ethernet, machines[0], nat);
      } else {
        for (auto && m : machines) {
          Interact(ethernet, m, {});
        }
      }
    } else {
      auto [dest, p] = ethernet.front();
      ethernet.pop_front();
      if (dest == 255) {
        nat = p;
        if (!part1) { part1 = p.second; }
      } else if (dest < 50) {
        Interact(ethernet, machines[dest], p);
      } else {
        throw std::runtime_error{"bad destination"};
      }
    }
  }

  std::cout << "Part 1: " << *part1 << std::endl;
  std::cout << "Part 2: " << *part2 << std::endl;
}