aocpp/2020/10.cpp

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

#include <doctest.h>

#include <aocpp/Startup.hpp>

namespace {

// Parses the numbers and returns them in sorted order
auto Parse(std::istream & in) -> std::vector<std::int64_t>
{
  std::vector<std::int64_t> result;
  std::int64_t value;
  while (in >> value) {
    result.push_back(value);
  }
  std::sort(result.begin(), result.end());
  return result;
}

auto Part1(std::vector<std::int64_t> const& adapters) -> std::size_t
{
  std::int64_t prev{0};
  std::size_t ones{0}, threes{1};
  if (adapters.empty()) return 0;
  for (auto const x : adapters) {
    switch (x - prev) {
    case 1: ones++; break;
    case 3: threes++; break;
    }
    prev = x;
  }
  return ones * threes;
}

auto Part2(std::vector<std::int64_t> const& adapters) -> std::size_t
{
  std::size_t n1{1}, n2{0}, n3{0};
  std::int64_t prev{0};

  for (auto const x : adapters) {
    switch(x - prev) {
      case 1:  std::tie(n1,n2,n3) = std::make_tuple(n1+n2+n3, n1, n2); break;
      case 2:  std::tie(n1,n2,n3) = std::make_tuple(n1+n2,     0, n1); break;
      case 3:  std::tie(n1,n2,n3) = std::make_tuple(n1,        0,  0); break;
      default: std::tie(n1,n2,n3) = std::make_tuple(0       ,  0,  0); break;
    }
    prev = x;
  }

  return n1;
}

} // namespace

TEST_SUITE("documented examples") {

TEST_CASE("part 1") {
  std::istringstream in {"16 10 15 5 1 11 7 19 6 12 4"};
  REQUIRE(Part1(Parse(in)) == 7*5);
  in = std::istringstream{"28 33 18 42 31 14 46 20 48 47 24 23 49 45 19 38 39 11 1 32 25 35 8 17 7 9 4 2 34 10 3 "};
  REQUIRE(Part1(Parse(in)) == 22*10);
}

TEST_CASE("part 2") {
  std::istringstream in {"16 10 15 5 1 11 7 19 6 12 4"};
  REQUIRE(8 == Part2(Parse(in)));
  in = std::istringstream{"28 33 18 42 31 14 46 20 48 47 24 23 49 45 19 38 39 11 1 32 25 35 8 17 7 9 4 2 34 10 3 "};
  REQUIRE(19208 == Part2(Parse(in)));
}

}

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