aocpp/2019/23.cpp

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

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

namespace {

struct Payload { ValueType x, y; };
struct Packet { ValueType destination; Payload payload; };
using Ethernet = std::deque<Packet>;
using Machines = std::array<Machine, 50>;

auto BuildNetwork(Machine m) -> Machines {
  Machines machines;
  auto& i = std::get<Input>(Step(m)).input;
  for (i = 0; i < std::int64_t(machines.size()); i++) {
    machines[i] = m;
  }
  return machines;
}

auto Interact(Ethernet & ethernet, Machine & m, std::optional<Payload> p) -> void {
  for(;;) {
    auto e = Step(m);
    switch (e.index()) {
      default: throw std::runtime_error{"unexpected halt"};
      case 0: {
        auto& i = std::get<0>(e).input;
        if (p) {
          i = p->x;
          StepInput(m, p->y);
          p = {};
          break;
        }
        i = -1; // no packet
        return;
      }
      case 1: {
        auto d = std::get<1>(e).output;
        auto x = StepOutput(m);
        auto y = StepOutput(m);
        ethernet.push_back({d, {x,y}});
      }
    }
  }
}

} // namespace

auto Main(std::istream & in) -> void
{
  auto machines = BuildNetwork(Machine{ParseStream(in)});
  auto ethernet = Ethernet{};

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

  for(;;) {
    if (!ethernet.empty()) {
      auto const packet = ethernet.front();
      ethernet.pop_front();
      if (packet.destination == 255) {
        nat = packet.payload;
        if (!part1) { part1 = packet.payload.y; }
      } else {
        Interact(ethernet, machines.at(packet.destination), packet.payload);
      }
    } else if (nat) {
      if (part2 == nat->y) { break; }
      part2 = nat->y;
      Interact(ethernet, machines[0], nat);
    } else {
      for (auto & m : machines) {
        Interact(ethernet, m, {});
      }
    }
  }

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