GATE | Gate IT 2007 | Question 30

Suppose you are given an implementation of a queue of integers. The operations that can be performed on the queue are:

i. isEmpty (Q) — returns true if the queue is empty, false otherwise.

ii. delete (Q) — deletes the element at the front of the queue and returns its value.

iii. insert (Q, i) — inserts the integer i at the rear of the queue.

Consider the following function:

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void f (queue Q) {
int i ;
if (!isEmpty(Q)) {
   i = delete(Q);
   f(Q);
   insert(Q, i);
  }
}

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What operation is performed by the above function f ?
(A) Leaves the queue Q unchanged
(B) Reverses the order of the elements in the queue Q
(C) Deletes the element at the front of the queue Q and inserts it at the rear keeping the other elements in the same order
(D) Empties the queue Q


Answer: (B)

Explanation: As it is recursive call, and removing from front while inserting from end, that means last element will be deleted at last and will be inserted 1st in the new queue. And like that it will continue till first call executes insert(Q,i) function.
So, the queue will be in reverse.


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