aoc-2021-solution-day1-part1.cc

uint32_t count_increasing_windows(std::istream &input) {
  auto sliding_window_view = std::ranges::istream_view<uint32_t>(input) 
    | std::ranges::views::transform([e1 = 0, e2 = 0, e3 = 0](uint32_t curr) mutable {
        e1 = std::exchange(e2, std::exchange(e3, curr));
        return e1 + e2 + e3;
        });

  return std::ranges::count_if(sliding_window_view, 
                               [prev = std::numeric_limits<uint32_t>::max(), drop = 2]
                               (uint32_t curr) mutable {
                                  if (drop > 0) {
                                    drop--;
                                    return false;
                                  }
                                  return std::exchange(prev, curr) < curr; });
}