aocpp/2016/01.cpp

#include <cstdint>
#include <iostream>
#include <sstream>
#include <stdexcept>
#include <unordered_map>
#include <vector>

#include <boost/phoenix.hpp>
#include <boost/range/irange.hpp>
#include <boost/spirit/include/qi.hpp>

#include <doctest.h>

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

namespace {

namespace phx = boost::phoenix;
namespace qi = boost::spirit::qi;

enum class Dir { L, R };

struct Command {
  Dir dir;
  std::size_t n;
};

using Input = std::vector<Command>;

// Input file grammar
class Grammar : public qi::grammar<std::string::const_iterator, Input(), qi::ascii::space_type> {
  qi::rule<iterator_type, Dir()> dir;
  qi::rule<iterator_type, Command(), qi::ascii::space_type> command;
  qi::rule<iterator_type, Input(), qi::ascii::space_type> commands;

public:
  Grammar() : Grammar::base_type{commands} {
    using namespace qi::labels;

    dir =
      qi::string("L") [ _val = Dir::L ] |
      qi::string("R") [ _val = Dir::R ];
    command = qi::lexeme[
      dir [ phx::bind(&Command::dir, _val) = _1] >>
      qi::ulong_long [ phx::bind(&Command::n, _val) = _1]
    ];
    commands = command % ",";
  }
};

auto Part1(Input const& input) -> std::int64_t
{
  auto here = aocpp::Coord{};
  auto face = aocpp::Coord{0,1};

  for (auto const& command : input) {
    switch (command.dir) {
      case Dir::R: face = aocpp::CW(face); break;
      case Dir::L: face = aocpp::CCW(face); break;
    }
    here += command.n * face;
  }

  return aocpp::Norm1(here);
}

auto Part2(Input const& input) -> std::int64_t
{
  auto seen = std::unordered_set<aocpp::Coord>{aocpp::Coord{0,0}};
  auto here = aocpp::Coord{0,0};
  auto face = aocpp::Coord{0,1};

  for (auto const& command : input) {
    switch (command.dir) {
      case Dir::R: face = aocpp::CW(face); break;
      case Dir::L: face = aocpp::CCW(face); break;
    }
    for (auto const _ : boost::irange(command.n)) {
      here += face;
      if (!seen.insert(here).second) {
        return aocpp::Norm1(here);
      }
    }
  }

  throw std::runtime_error{"no solution to part 2"};
}

} // namespace

TEST_SUITE("2016-01 examples") {
  TEST_CASE("example 1") {
    auto in = std::istringstream{"R2, L3"};
    auto const commands = aocpp::ParseGrammar_(Grammar{}, in);
    CHECK(5 == Part1(commands));
  }
  TEST_CASE("example 2") {
    auto in = std::istringstream{"R2, R2, R2"};
    auto const commands = aocpp::ParseGrammar_(Grammar{}, in);
    CHECK(2 == Part1(commands));
  }
  TEST_CASE("example 3") {
    auto in = std::istringstream{"R5, L5, R5, R3"};
    auto const commands = aocpp::ParseGrammar_(Grammar{}, in);
    CHECK(12 == Part1(commands));
  }
  TEST_CASE("example 4") {
    auto in = std::istringstream{"R8, R4, R4, R8"};
    auto const commands = aocpp::ParseGrammar_(Grammar{}, in);
    CHECK(4 == Part2(commands));
  }
}

auto Main(std::istream & in, std::ostream & out) -> void
{
  auto const input = aocpp::ParseGrammar_(Grammar{}, in);
  out << "Part 1: " << Part1(input) << std::endl;
  out << "Part 2: " << Part2(input) << std::endl;
}