Answer by
Melody22 (9)

Quicksort is a comparison sort and, in efficient implementations, is not a stable sort.
Quicksort is a well-known sorting algorithm developed by C. a. r. Hoare that, makes \mathcal{O}(n\log n comparisons to sort n items. The worst case, it makes \mathcal{O}(n^2) comparisons, though if implemented correctly this behavior is rare.