Function RunLengthEncode

src/common/numeric.h:33–45

 */
template <typename Iter, typename Idx>
void RunLengthEncode(Iter begin, Iter end, std::vector<Idx>* p_out) {
  auto& out = *p_out;
  out = std::vector<Idx>{0};
  size_t n = std::distance(begin, end);
  for (size_t i = 1; i < n; ++i) {
    if (begin[i] != begin[i - 1]) {
      out.push_back(i);
    }
  }
  if (out.back() != n) {
    out.push_back(n);
  }
}

/**
 * @brief Variant of std::partial_sum, out_it should point to a container that has n + 1