Quick Sort

int partition(std::vector<int>& arr, size_t start, size_t end)
{
    int x = arr[start];
    int i = start;
    for(size_t j = start + 1; j < end; j++)
    {
        if(arr[j]<=x)
      {
            i=i+1;
          std::swap(arr[i], arr[j]);
        }
    }
    std::swap(arr[i], arr[start]);
    return i;
}
void quick_sort(std::vector<int>& arr, size_t start, size_t end)
{
    if(start < end)
    {
        int pivot = partition(arr, start, end);
        quick_sort(arr, start, pivot);
        quick_sort(arr, pivot + 1, end);
    }
}