What is the worst case scenario for quicksort?

Question

When does the quicksort algorithm take O(n^2) time?

Answer 1

The factors that contribute to the worst-case scenario of quicksort are as follows:

• Worst case occurs when the subarrays are completely unbalanced
• The worst case occurs when there are 0 elements in one subarray and n-1 elements in the other.

In other words, the worst-case running time of quicksort occurs when Quicksort takes in a sorted array (in decreasing order), to be on the time complexity of O(n^2).