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Data Structures | Queue | Question 1

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Following is C like pseudo-code of a function that takes a Queue as an argument, and uses a stack S to do processing. 


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));

What does the above function do in general?


Removes the last from Q


Keeps the Q same as it was before the call


Makes Q empty


Reverses the Q

Answer: (D)


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 the stack is LIFO order, all items of the queue are reversed.

Hence option (D) is the correct answer.

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Last Updated : 08 Jan, 2013
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