aocpp/2019/24.cpp

#include <algorithm>
#include <concepts>
#include <cstdint>
#include <iostream>
#include <iterator>
#include <map>
#include <set>
#include <stdexcept>
#include <string>
#include <tuple>
#include <vector>

#include <aocpp/Startup.hpp>
#include <aocpp/Coord.hpp>

using namespace aocpp;

namespace {

struct Map {
  std::vector<std::string> rows;

  auto operator[](Coord c)       -> char& { return rows[c.y][c.x]; }
  auto operator[](Coord c) const -> char  { return rows[c.y][c.x]; }

  static auto Parse(std::istream & in) -> Map {
    Map result;
    std::string line;
    while (std::getline(in, line)) {
      result.rows.emplace_back(std::move(line));
    }
    return {result};
  }
};

auto FindBugs(Map const& map) {
  std::vector<Coord> result;

  std::int64_t w = map.rows[0].size();
  std::int64_t h = map.rows.size();

  for (std::int64_t x = 0; x < w; x++) {
    for (std::int64_t y = 0; y < h; y++) {
      Coord const c = {x,y};
      if (map[c] == '#') result.push_back(c);
    }
  }
  return result;
}

struct Neighbor1 {
  auto operator()(Coord c, auto f) const -> void {
    if (c.x > 0) f(Left(c));
    if (c.x < 4) f(Right(c));
    if (c.y > 0) f(Up(c));
    if (c.y < 4) f(Down(c));
  }
};

struct Neighbor2 {
  using C3 = std::pair<Coord, std::int64_t>;
  auto operator()(C3 cd, auto f) const -> void {
    auto const [c,d] = cd;

    auto left_neighbors = [&f](Coord c, std::int64_t d, auto k_, auto k) {
      c = k_(c);
      if (c.x == 1 && c.y == 0) {
        for (std::int64_t yi = -2; yi <= 2; yi++) {
          f({k({2,yi}),d+1});
        }
      } else if (c.x > -2) {
        f({k(Left(c)),d});
      } else {
        f({k({-1,0}),d-1});
      }
    };
    auto id = [](Coord i) { return i; };
    left_neighbors(c, d, id, id);
    left_neighbors(c, d, Turn180, Turn180);
    left_neighbors(c, d, CW, CCW);
    left_neighbors(c, d, CCW, CW);
  }
};

template<typename F, typename C>
auto Step(std::vector<C> const& bugs, F with_neighbors = F{})
{
  std::map<C, int> adjacent;
  for (auto const& x : bugs) {
    with_neighbors(x, [&adjacent](C n) -> void { adjacent[n]++; });
  }

  std::vector<C> result;
  for (auto const& [k,v] : adjacent) {
    switch (v) {
    case 1:
      result.push_back(k);
      break;
    case 2:
      if (!std::binary_search(bugs.begin(), bugs.end(), k)) {
        result.push_back(k);
        break;
      }
    }
  }

  return result;
}

auto Bio(std::vector<Coord> const& bugs) -> std::uint32_t {
  std::uint32_t result = 0;
  for (auto const& c : bugs) {
    result |= 1U << (5 * c.y + c.x);
  }
  return result;
}

auto Part1(std::vector<Coord> const& bugs) -> std::uint32_t {
  auto cursor = bugs;
  std::set<std::uint32_t> seen;
  std::uint32_t bio;
  while (seen.insert(bio = Bio(cursor)).second) {
    cursor = Step<Neighbor1>(cursor);
  }
  return bio;
}

auto Part2(std::vector<Coord> const& bugs) {
  std::vector<std::pair<Coord,std::int64_t>> bugs2;
  for (auto const& [x,y] : bugs) {
    bugs2.push_back({{x-2,y-2},0});
  }
  for (int i = 0; i < 200; i++) {
    bugs2 = Step<Neighbor2>(bugs2);
  }
  return bugs2.size();
}

} // namespace

auto main(int argc, char** argv) -> int {
  auto const bugs = FindBugs(Map::Parse(Startup(argc, argv)));
  std::cout << "Part 1: " << Part1(bugs) << std::endl;
  std::cout << "Part 2: " << Part2(std::move(bugs)) << std::endl;
}