aocpp/2022/12.cpp

#include <cstdint>
#include <iostream>
#include <optional>
#include <set>
#include <sstream>
#include <tuple>
#include <vector>

#include <doctest.h>

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

using aocpp::Coord;
using aocpp::Grid;

namespace {

auto Parse(std::istream & in) -> std::tuple<Coord, std::vector<Coord>, Coord, Grid>
{
  Coord start1 {};
  std::vector<Coord> starts2;
  Coord end {};
  auto grid = Grid::Parse(in);

  grid.each([&](Coord c, char v) {
    switch (v) {
      case 'S': grid[c] = 'a'; start1 = c; break;
      case 'E': grid[c] = 'z'; end   = c; break;
      case 'a': starts2.push_back(c);     break;
    }
  });

  return {start1, std::move(starts2), end, std::move(grid)};
}

auto Solve(std::vector<Coord> starts, Coord end, Grid const& grid) -> std::optional<std::int64_t>
{
  std::vector<Coord> next_layer;
  std::set<Coord> seen;
  std::int64_t counter {1};

  while (!starts.empty()) {
    for (auto here : starts) {
      if (!seen.insert(here).second) continue;
      auto here_height = grid[here];
      for (auto next : {Up(here), Down(here), Left(here), Right(here)}) {
        if (!grid.contains(next)) continue;
        if (grid[next] - 1 > here_height) continue;
        if (next == end) { return counter; }
        next_layer.push_back(next);
      }
    }
    counter++;
    starts.clear();
    std::swap(starts, next_layer);
  }

  return {};
}

} // namespace

TEST_SUITE("2022-12 examples") {
  TEST_CASE("documented example") {
    std::istringstream in {
      "Sabqponm\n"
      "abcryxxl\n"
      "accszExk\n"
      "acctuvwj\n"
      "abdefghi\n"
    };
    auto [start1, starts2, end, grid] = Parse(in);
    CHECK(31 == Solve({start1}, end, grid));
    CHECK(29 == Solve(std::move(starts2), end, grid));
  }
}

auto Main(std::istream & in, std::ostream & out) -> void
{
  auto [start1, starts2, end, grid] = Parse(in);
  out << "Part 1: " << Solve({start1}, end, grid).value_or(-1) << std::endl;
  out << "Part 2: " << Solve(std::move(starts2), end, grid).value_or(-1) << std::endl;
}