aocpp/2020/03.cpp

#include <algorithm>
#include <cstdint>
#include <iostream>
#include <sstream>
#include <tuple>
#include <cstdio>
#include <cstdlib>
#include <numeric>
#include <functional>

#include <doctest.h>

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

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

namespace {

auto Ski(Grid const& grid, Coord step) -> std::size_t
{
  std::size_t const w = grid.Cols();
  std::size_t const h = grid.Rows();
  std::size_t trees {0};
  Coord here {0,0};

  while(here.y < h) {
    if (grid[here] == '#') trees++;
    here += step;
    while (here.x >= w) { here.x -= w; }
  }
  return trees;
}

auto Part1(Grid const& grid) {
  return Ski(grid, {3,1});
}

auto Part2(Grid const& grid) {
  Coord const slopes[] = {{1,1}, {3,1}, {5,1}, {7,1}, {1,2}};
  return std::transform_reduce(
    std::begin(slopes), std::end(slopes),
    1ULL, std::multiplies(),
    [&](Coord slope) { return Ski(grid, slope); });
}

} // namespace

TEST_SUITE("documented examples") {

std::istringstream in {
  "..##.......\n"
  "#...#...#..\n"
  ".#....#..#.\n"
  "..#.#...#.#\n"
  ".#...##..#.\n"
  "..#.##.....\n"
  ".#.#.#....#\n"
  ".#........#\n"
  "#.##...#...\n"
  "#...##....#\n"
  ".#..#...#.#\n"
};
auto grid = Grid::Parse(in);

TEST_CASE("part 1") {
  REQUIRE(Part1(grid) == 7);
}

TEST_CASE("part 2") {
  REQUIRE(Part2(grid) == 336);
}

}

auto Main(std::istream & in, std::ostream & out) -> void
{
  auto const grid {Grid::Parse(in)};
  out << "Part 1: " << Part1(grid) << std::endl;
  out << "Part 2: " << Part2(grid) << std::endl;
}