GATE Data Science and Artificial Intelligence 2024 | Sample Paper | Question: 50

Question

Assume that $\text{S}$ is a stack and $\text{Q1}$ and $\text{Q2}$ are two Queues which support the Enqueue and Dequeue operations. Consider the following pseudo code for implementing the Pop and Push operation on $\text{S}$.
 

Push(S,x)
      A(Q2,x)
      while(Q1 not empty)
             B(Q2,C(Q1));
      Swap(Q1,Q2)
Pop(S)
      return(D(Q1))

Which of the following options for the functions $\text{A, B, C}$, and $\text{D}$ would correspond to correctly implementing the Push and Pop operations on the stack $\text{S}$?

1. $\text{A, B}$ - Enqueue $\text{C, D}$ - Dequeue
2. $\text{A, C}$ - Enqueue $\text{B, D}$ - Dequeue
3. $\text{A, C}$ - Dequeue $\text{B, D}$- Enqueue
4. $\text{A, D}$ - Enqueue $\text{B, C}$ - Dequeue

Answer 1

(A) A,B - Enqueue C,D - Dequeue

Answer 2

The correct functions for implementing the Push and Pop operations on stack S using queues Q1 and Q2 are:

A: Enqueue B: Enqueue C: Dequeue D: Dequeue

Here's how the code works with these functions:

Push(S, x):

1. Enqueue(Q2, x): Adds the new element x to the back of Q2.
2. while(Q1 not empty): Transfers all elements from Q1 to Q2, preserving their order:
   • Dequeue(Q1): Removes the front element from Q1.
   • Enqueue(Q2, ...): Adds the removed element to the back of Q2.
3. Swap(Q1, Q2): Exchanges Q1 and Q2, making Q1 hold the elements in the correct stack order.

Pop(S):

1. Dequeue(Q1): Removes and returns the front element from Q1, which is the top element of the simulated stack.

Answer 3

Ans A) if you see carefully they already gave answer in question , Enqueue op. need two argument (one for queue and second for element ) and dequeue need one argument (queue only) so pretty much simple .