Is imperative Quicksort in situ (in-place) or not?

Question

Quicksort is often described as an in situ (in-place) algorithm, despite the fact that it requires O(log n) stack space. So does in situ mean \"requires le

Answer 1

is Quicksort actually not an in situ algorithm?

The standard implementation of it is not in situ. It's a horribly common misconception, but you as correctly note due to stack space consumption, that conception is wrong.

I say "standard implementation" of it because people have modified the algorithm to make it an O(1)-space algorithm. Here is one example: Quicksort without a stack.

Of course, consistent with the classic space-time tradeoff, such versions of quicksort are less performant than the standard implementation.