aocpp/2022/12.cpp

#include <cstdint>
#include <iostream>
#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, Coord, Grid>
{
  Coord start {};
  Coord end {};
  auto grid = Grid::Parse(in);

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

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

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

  while (!prev_layer.empty()) {
    for (auto here : prev_layer) {
      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] - here_height > 1) continue;
        if (next == end) { return counter; }
        next_layer.push_back(next);
      }
    }
    counter++;
    prev_layer.clear();
    std::swap(prev_layer, next_layer);
  }

  return -1;
}

auto Part2Starts(Grid const& grid) -> std::vector<Coord>
{
    std::vector<Coord> starts;
    grid.each([&](Coord c, char v) {
      if (v == 'a') starts.push_back(c);
    });
    return starts;
}

} // namespace

TEST_SUITE("2022-12 examples") {
  TEST_CASE("documented example") {
    std::istringstream in {
      "Sabqponm\n"
      "abcryxxl\n"
      "accszExk\n"
      "acctuvwj\n"
      "abdefghi\n"
    };
    auto [start, end, grid] = Parse(in);
    CHECK(31 == Solve({start}, end, grid));
    CHECK(29 == Solve(Part2Starts(grid), end, grid));
  }
}

auto Main(std::istream & in) -> void
{
  auto const [start, end, grid] = Parse(in);
  std::cout << "Part 1: " << Solve({start}, end, grid) << std::endl;
  std::cout << "Part 2: " << Solve(Part2Starts(grid), end, grid) << std::endl;
}