AoC 2022 day 9

#include "2022_utils.h"

using namespace std;

namespace {
  template <typename T> int sgn(T val) {
    return (T(0) < val) - (val < T(0));
  }

  auto part1() {
    auto s = load_strings("2022/2022_day09_input.txt");
    int64_t result = 0;

    using P = pair<int, int>;
    set<P> all_tail_pos;

    P head_pos{ 0, 0, };
    P tail_pos{ 0, 0, };
    all_tail_pos.insert(tail_pos);
    for (auto& ss : s) {
      char dir;
      int steps;
      sscanf_s(ss.c_str(), "%c %d", &dir, 1, &steps);

      for (int i = 0; i < steps; ++i) {
        switch (dir) {
        case 'R': {
          head_pos.first += 1;
        }break;
        case 'L': {
          head_pos.first -= 1;
        } break;
        case 'U': {
          head_pos.second -= 1;
        } break;
        case 'D': {
          head_pos.second += 1;
        } break;
        };

        int tail_to_head_x = head_pos.first - tail_pos.first;
        int tail_to_head_y = head_pos.second - tail_pos.second;
        if (abs(tail_to_head_x) >= 2 || abs(tail_to_head_y) >= 2) {
          tail_pos.first += sgn(tail_to_head_x);
          tail_pos.second += sgn(tail_to_head_y);
        }
        all_tail_pos.insert(tail_pos);
      }
    }

    return all_tail_pos.size();
  }

  auto part2() {
    auto s = load_strings("2022/2022_day09_input.txt");
    int64_t result = 0;

    using P = pair<int, int>;
    set<P> all_tail_pos;

    vector<P> rope(10, P{0, 0});
    all_tail_pos.insert(rope.back());
    for (auto& ss : s) {
      char dir;
      int steps;
      sscanf_s(ss.c_str(), "%c %d", &dir, 1, &steps);

      for (int i = 0; i < steps; ++i) {
        switch (dir) {
        case 'R': {
          rope[0].first += 1;
        } break;
        case 'L': {
          rope[0].first -= 1;
        } break;
        case 'U': {
          rope[0].second -= 1;
        } break;
        case 'D': {
          rope[0].second += 1;
        } break;
        };

        for (int i = 0; i < rope.size() - 1; ++i) {
          int tail_to_head_x = rope[i].first - rope[i + 1].first;
          int tail_to_head_y = rope[i].second - rope[i + 1].second;
          if (abs(tail_to_head_x) >= 2 || abs(tail_to_head_y) >= 2) {
            rope[i + 1].first += sgn(tail_to_head_x);
            rope[i + 1].second += sgn(tail_to_head_y);
          }
        }
        all_tail_pos.insert(rope.back());
      }
    }

    return all_tail_pos.size();
  }
}

namespace y2022 {
  void day09() {
    cout << "part 1: " << part1() << "\n";
    cout << "part 2: " << part2() << "\n";
  }
}