This is a tempest in a teapot. There's no data on the stack as Quicksort proceeds, only indices to data, so by one definition, Quicksort is in-place. But if an

This is a tempest in a teapot. There's no data on the stack as Quicksort proceeds, only indices to data, so by one definition, Quicksort is in-place. But if an algorithm is judged by how much stack it uses, many algorithms that we think of as in-place aren't.