aocpp/2019/24.cpp

#include <algorithm>
#include <cstdint>
#include <iostream>
#include <iomanip>
#include <fstream>
#include <iterator>
#include <stdexcept>
#include <vector>
#include <set>
#include <string>
#include <tuple>
#include <bitset>
#include <deque>
#include <cctype>
#include <queue>
#include <map>

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

using namespace aocpp;

namespace {

Coord(* const directions[4])(Coord) = {Up, Down, Left, Right};

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::set<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.insert(c);
    }
  }
  return result;
}

auto Neighbor1(Coord c) {
  std::vector<Coord> result;
  result.reserve(4);
  if (c.x > 0) result.push_back({c.x-1,c.y});
  if (c.x < 4) result.push_back({c.x+1,c.y});
  if (c.y > 0) result.push_back({c.x,c.y-1});
  if (c.y < 4) result.push_back({c.x,c.y+1});
  return result;
}

auto Neighbor2(std::pair<Coord, std::int64_t> cd) {
  auto [c,d] = cd;
  std::vector<std::pair<Coord, std::int64_t>> result;
  result.reserve(8);

  if (c.x == 3 && c.y == 2) {
    for (std::int64_t yi = 0; yi < 5; yi++) {
      result.push_back({{4,yi},d+1});
    }
  } else if (c.x > 0) {
    result.push_back({{c.x-1,c.y},d});
  } else {
    result.push_back({{1,2},d-1});
  }

  if (c.x == 1 && c.y == 2) {
    for (std::int64_t yi = 0; yi < 5; yi++) {
      result.push_back({{0,yi},d+1});
    }
  } else if (c.x < 4) {
    result.push_back({{c.x+1,c.y},d});
  } else {
    result.push_back({{3,2},d-1});
  }

  if (c.x == 2 && c.y == 3) {
    for (std::int64_t xi = 0; xi < 5; xi++) {
      result.push_back({{xi,4},d+1});
    }
  } else if (c.y > 0) {
    result.push_back({{c.x,c.y-1},d});
  } else {
    result.push_back({{2,1},d-1});
  }

  if (c.x == 2 && c.y == 1) {
    for (std::int64_t xi = 0; xi < 5; xi++) {
      result.push_back({{xi,0},d+1});
    }
  } else if (c.y < 4) {
    result.push_back({{c.x,c.y+1},d});
  } else {
    result.push_back({{2,3},d-1});
  }

  return result;
}

template<class F, class C>
auto Step(std::set<C> const& bugs, F const& neighbors)
{
  std::map<C, int> adjacent;
  for (auto const& x : bugs) {
    for (auto const& n : neighbors(x)) {
      adjacent[n]++;
    }
  }

  std::set<C> result;
  for (auto const& [k,v] : adjacent) {
    switch (v) {
      case 1: result.insert(k); break;
      case 2: if (!bugs.contains(k)) result.insert(k); break;
    }
  }

  return result;
}

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

auto Part1(std::set<Coord> const& bugs) {
  std::int64_t n = 0;
  auto cursor = bugs;
  std::set<std::uint32_t> seen;
  while (seen.insert(Bio(cursor)).second) {
    n++;
    cursor = Step(cursor, Neighbor1);
  }
  return Bio(cursor);
}

auto Part2(std::set<Coord> const& bugs) {
  std::set<std::pair<Coord,std::int64_t>> bugs2;
  for (auto const& x : bugs) {
    bugs2.insert({x,0});
  }
  for (int i = 0; i < 200; i++) {
    bugs2 = Step(bugs2, Neighbor2);
  }
  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;
}