There are few cases for which QuickSort becomes "Slowsort", with complexity of O(n2). Consider, for example, what happens if the value picked each time as the partitioning value happens to be the largest, or smallest, value in the array. In general, however, it has performance roughly O(nlog2n). It was noted that if the partitions did not divide the list into roughly equal parts, this sort would lose efficiency. In fact, the worst possible case is a list that starts out already sorted, for each partition will have an empty left sub-list and all but the one element in the right. Quicksort degenerates into a slowsort in such cases.
