aoc2024/day21/try_split_sequence.cc

#include "try_split_sequence.h"

#include <vector>

std::optional<std::pair<std::string_view, std::string_view>>
TrySplitSequence(const std::string_view &sequence) {
  std::vector<size_t> a_keys;
  for (size_t i = 0; i < sequence.size(); ++i) {
    if (sequence[i] == 'A') {
      a_keys.push_back(i);
    }
  }

  if (a_keys.size() < 2) {
    return std::nullopt;
  }

  size_t midpoint = a_keys.size() / 2 - 1;
  return std::make_pair(std::string_view(&(sequence[0]), a_keys[midpoint]+1),
                        std::string_view(&(sequence[a_keys[midpoint]+1]),
                                         sequence.size() - a_keys[midpoint]-1));
}