aocpp/2022/01.cpp

#include <algorithm>
#include <cstdint>
#include <iostream>
#include <numeric>
#include <sstream>
#include <stdexcept>
#include <string>
#include <tuple>
#include <vector>

#include <doctest.h>

#include <aocpp/Startup.hpp>

namespace {

using Input = std::vector<std::vector<std::int64_t>>;

/// @brief Parse the input stream as a newline-delimited list of lists of integers
/// @param in input file parsed until EOF
/// @return outer list of elves, inner lists of calories
auto Parse(std::istream & in) -> Input
{
  Input result {{}};
  std::string line;
  while (std::getline(in, line)) {
    if (line.empty()) {
      result.push_back({});
    } else {
      result.back().emplace_back(std::stoll(line));
    }
  }
  return result;
}

/// @brief Compute the top calorie carrying elves
/// @param input List of elves each with a list of calories
/// @return top 1 and sum of top 3 calorie counts
auto Solve(Input const& input) -> std::pair<std::int64_t, std::int64_t>
{
  if (input.size() < 3) {
    throw std::runtime_error{"bad input"};
  }

  std::vector<std::int64_t> elves;
  std::transform(
    input.begin(), input.end(), std::back_inserter(elves),
    [](auto const& elf){
      return std::reduce(elf.begin(), elf.end());
    });

  // Fill the top 3 array elements with the maximum values
  auto const top3 = std::next(elves.begin(), 3);
  std::partial_sort(elves.begin(), top3, elves.end(), std::greater());

  auto const p1 = elves.front();
  auto const p2 = std::reduce(elves.begin(), top3);
  return {p1, p2};
}

} // namespace

TEST_SUITE("2022-01 examples") {
  TEST_CASE("example") {
    std::istringstream in {
      "1000\n"
      "2000\n"
      "3000\n"
      "\n"
      "4000\n"
      "\n"
      "5000\n"
      "6000\n"
      "\n"
      "7000\n"
      "8000\n"
      "9000\n"
      "\n"
      "10000\n"};
    auto const entries = Parse(in);
    auto const [p1,p2] = Solve(entries);
    CHECK(p1 == 24000);
    CHECK(p2 == 45000);
  }
}

auto Main(std::istream & in, std::ostream & out) -> void
{
  auto const [p1,p2] = Solve(Parse(in));
  out << "Part 1: " << p1 << std::endl;
  out << "Part 2: " << p2 << std::endl;
}