Candidate solutions sent after the fact

solutions.cpp

int solution(std::vector<int> &A, std::vector<int> &B)
{
  std::map<int, int> disjoints;

  for (std::size_t i = 0; i < A.size(); ++i)
  {
    auto it = disjoints.lower_bound(B[i]);
    if (it == disjoints.end())
    {
      disjoints.emplace(A[i], B[i]);
    }
    else
    {
        if (B[i] >= it->first && A[i] <= it->second)
        {
          std::pair<int, int> new_pair(std::min(it->first, A[i]), std::max(it->second, B[i]));
          disjoints.erase(it);
          disjoints.emplace(new_pair.first, new_pair.second);
        }
        else if (it != disjoints.begin())
        {
          --it;
          if (B[i] >= it->first && A[i] <= it->second)
          {
            std::pair<int, int> new_pair(std::min(it->first, A[i]), std::max(it->second, B[i]));
            disjoints.erase(it);
            disjoints.emplace(new_pair.first, new_pair.second);
          }
          else
          {
            disjoints.emplace(A[i], B[i]);
          }
        }
        else
        {
          disjoints.emplace(A[i], B[i]);
        }
    }
  }

  return disjoints.size();
}

int solution2(int x, std::vector<int> &arr)
{
  std::size_t total_equal_to = 0;
  for (std::size_t i = 0; i < arr.size(); ++i)
  {
    if (arr[i] == x)
      ++total_equal_to;
  }
  std::size_t total_not_equal_to = arr.size() - total_equal_to;

  std::size_t left_equal_to = 0;
  for (std::size_t i = 0; i < arr.size(); ++i)
  {
    if (arr[i] == x)
      ++left_equal_to;

    std::size_t left_not_equal_to = (i + 1) - left_equal_to;
    std::size_t right_not_equal_to = total_not_equal_to - left_not_equal_to;

    if (left_equal_to == right_not_equal_to) // I had typo here before
      return i + 1;
  }

  return -1; // Does not exist. Should never happen.
}