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BARC 2026 CS | Memory Based Questions | GO Classes | Question: 6

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Consider the following function:

void f(stack S) {
int x ;
if (!isEmpty(S)) {
        x = pop(S);
        f(S);
        push(S, x);
    }
}

What operation is performed by the above function $f$?

  1. Leaves the stack $S$ unchanged
     
  2. Reverses the order of the elements in the stack $S$
     
  3. Pops the top element of stack $S$
     
  4. Empties the stack $S$

1 Answer

2 2 votes

If Stack $S = [1, 2]$ (top is 2):

  • Call 1: Pop 2, store $x=2$. Call f(S).

  • Call 2: Pop 1, store $x=1$. Call f(S).

  • Call 3: Stack is empty. Return.

  • Back to Call 2: push(S, 1). Stack is now $[1]$.

  • Back to Call 1: push(S, 2). Stack is now $[1, 2]$.

The stack ends in its original state.

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