GATE IT 2007 | Question: 30

Question

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

1. $isEmpty (Q)$ — returns true if the queue is empty, false otherwise.
2. $delete (Q)$ — deletes the element at the front of the queue and returns its value.
3. $insert (Q, i)$ — inserts the integer i at the rear of the queue.

Consider the following function:

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

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 $Q$

Comments

I think the program will never come to execute insert(Q, i) operation because the program recurse before it and as it become empty the isEmpty() becomes true and if section becomes false and it should not enter that setion and terminates.

Kindly tell me where I am wrong.

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i also have the same doubt, initially it goes on deleting the elements from the queue and then the loop condition becomes false. So how are we executing the insert(q,i) statement...

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@Anand Mundhe

According to me,

implementing using arrays : call by reference is default.

implementing using linked list : you are sending a pointer of the queue, which is also call by reference.

So I think we don’t have to worry about call by value here

Answer 1

Hope it helps…

Plz Do upvote if you got it.

Answer 2

Hope it helps… Do upvote if you got it :)

Thank you.

Answer 3

Answer: B

Comments

Suppose 1 2 3 these 3 elements are in the queue. After deleting 1 2 then 3 it checks the condition isempty() which is false so insert (q,i) can't be called. So how insert function is getting called?