Suppose we are sorting an array of eight integers using quicksort, and we have just finished the first partitioning with the array looking like this:

2  5  1  7  9  12  11  10 

Which statement is correct?
(A) The pivot could be either the 7 or the 9.
(B) The pivot could be the 7, but it is not the 9
(C) The pivot is not the 7, but it could be the 9
(D) Neither the 7 nor the 9 is the pivot.


Answer: (A)

Explanation: 7 and 9 both are at their correct positions (as in a sorted array). Also, all elements on left of 7 and 9 are smaller than 7 and 9 respectively and on right are greater than 7 and 9 respectively.

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