ShakerSort.cpp

void ShakerSort(vector<int>& values) {
  if (values.empty()) {
    return;
  }
  int left = 0;
  int right = values.size() - 1;
  while (left <= right) {
    for (int i = right; i > left; --i) {
      if (values[i - 1] > values[i]) {
        swap(values[i - 1], values[i]);
      }
    }
    ++left;
    for (int i = left; i < right; ++i) {
      if (values[i] > values[i + 1]) {
        swap(values[i], values[i + 1]);
      }
    }
    --right;
  }
}

Why there is left <= right in line 7, not left < right? Should we do a loop, when both left and right point at the same element?