Algorithms Quiz | SP Contest 3 | Question 4

What does the below function do in general? 

C

void fun(Queue *Q)
{
    Stack S; // Say it creates an empty stack S

    // Run while Q is not empty
    while (!isEmpty(Q))
    {
        // deQueue an item from Q and
        // push the dequeued item to S
        push(&S, deQueue(Q));
    }

    // Run while Stack S is not empty
    while (!isEmpty(&S))
    {
    // Pop an item from S and enqueue
    // the popped item to Q
    enQueue(Q, pop(&S));
    }
}

(A)

Removes the last element from the queue, Q

(B)

Keeps the queue, Q same as it was before the call

(C)

Makes queue Q empty

(D)

Reverses the queue Q

Answer: (D)
Explanation:

The function takes a queue Q as an argument. It dequeues all items of Q and pushes them to a stack S. Then pops all items of S and enqueues the items back to Q. Since stack is LIFO order, all items of the queue are reversed.

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