ISRO | ISRO CS 2015 | Question 11

If the sequence of operations – push (1), push (2), pop, push (1), push (2), pop, pop, pop, push (2), pop are performed on a stack, the sequence of popped out values

(A)

2,2,1,1,2

(B)

2,2,1,2,2

(C)

2,1,2,2,1

(D)

2,1,2,2,2

Answer: (A)
Explanation:

Let’s simulate the sequence of operations on a stack:

Push(1): Stack = [1]
Push(2): Stack = [1, 2]
Pop: Pop 2, Stack = [1]
Push(1): Stack = [1, 1]
Push(2): Stack = [1, 1, 2]
Pop: Pop 2, Stack = [1, 1]
Pop: Pop 1, Stack = [1]
Pop: Pop 1, Stack = []
Push(2): Stack = [2]
Pop: Pop 2, Stack = []
The sequence of popped out values is: 2, 2, 1, 1, 2.

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