queue datastructure

Question

Consider the following code to reverse the elements of the Queue

1.  

1.   temp=dequeue(Queue);
   enqueue(temp,Queue);
   Reverse(Queue);
2.   Reverse(dequeue(Queue));
   temp=dequeue(Queue);
   enqueue(temp,Queue);
3.   temp=dequeue(Queue);
   Reverse(Queue);
   enqueue(temp,Queue);
4.   None of above

Comments

3.

Draw recursion tree. It'll help.

This is how 1 will execute.

In 2, we are passing element from a queue as an argument which will probably throw error.

And this is how 3 will execute.

Answer 1

                                                  Recursive algorithm for reversing the queue 

1. Pop the element from the queue if it is not empty, otherwise, return empty queue

2. call reverse(queue) for remaining queue

3. push the popped element in the queue 

 

1

2

3

4

after reversing we get,

4

3

2

1

temp = dequeue(Queue)

Reverse(Queue)

enqueue(temp , Queue)