Question

Consider the Quick sort algorithm which sorts elements in ascending order using the first element as pivot. Then which of the following input sequence will require a maximum number of comparisons when this algorithm is applied on it?

(a) 22 25 56 67 89

(b) 52 25 76 67 89

(c) 22 25 76 67 50

(d) 52 25 89 67 76

This question was addressed to me in examination.

Enquiry is from Quicksort in section Sorting of Data Structures & Algorithms II

Answer 1

Right option is (a) 22 25 56 67 89

Easy explanation - If the input sequence is already sorted then worst case behaviour occurs for the Quick sort algorithm which use the first element as pivot. Therefore, the input sequence given in 22 25 56 67 89 will require a maximum number of comparisons.