GATE | GATE CS 1996 | Question 40

Quicksort is run on two inputs shown below to sort in ascending order taking the first element as pivot,

(i) 1, 2, 3,......., n
(ii) n, n-1, n-2,......, 2, 1 

Let C₁ and C₂ be the number of comparisons made for the inputs (i) and (ii) respectively. Then,

(A)

C1 < C2 

(B)

C1 > C2

(C)

C1 = C2

(D)

We cannot say anything for arbitrary n

Answer: (C)

Explanation:

Quick Sort performs in the worst case when input is sorted in either ascending order or descending order. So, quick sort will return equal number of comparisons for both given inputs. Option (C) is correct.

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