Solution

The correct answer is option 2.

Explanation:

Operations of Dequeue :

•    AddFront : adding item to front of the queue.
•   AddRear : adding item to the rear of the queue.
•   RemoveFront : removing item from the front of the queue.
•   RemoveRear : removing item from the rear of the queue.

Stack has two operations : PUSH - to insert data into stack. POP - to delete an element from stack. It supports LIFO(Last In First Out) .

AddFront() is same as PUSH operation, therefore , the time complexity is O(1).

To perform AddRear() operation, using stack  we need two operations , PUSH(POP()) all the elements of the stack. Therefore, the time complexity is O(n).