Implementing Queue with Two Stacks

Your task is to implement a queue using two stacks. You are provided with ‘Q’ queries and need to handle them, where each query falls under one of these two operations:

Enqueue an element ‘X’ to the end of the queue.

Dequeue an element from the front of the queue.

Functionality:

For enqueue, return true after the element is enqueued.

For dequeue, return -1 if the queue is empty, otherwise return the dequeued element.

Example:

Input:

5
1 10
1 20
2
1 30
2

Output:

true
true
10
true
20

Explanation:

The given queries perform the following operations:

Enqueue 10: Returns true

Enqueue 20: Returns true

Dequeue: Returns 10 (dequeued)

Enqueue 30: Returns true

Dequeue: Returns 20 (dequeued)

Constraints:

1

Question

Implementing Queue with Two Stacks

Your task is to implement a queue using two stacks. You are provided with ‘Q’ queries and need to handle them, where each query falls under one of these two operations:

Enqueue an element ‘X’ to the end of the queue.
Dequeue an element from the front of the queue.

Functionality:

For enqueue, return true after the element is enqueued.
For dequeue, return -1 if the queue is empty, otherwise return the dequeued element.

Example:

Input:

Output:

true
true
10
true
20

Explanation:

The given queries perform the following operations:

Enqueue 10: Returns true
Enqueue 20: Returns true
Dequeue: Returns 10 (dequeued)
Enqueue 30: Returns true
Dequeue: Returns 20 (dequeued)

Constraints:

1 <= Q <= 10^5
1 <= P <= 2
1 <= X <= 10^5 (for enqueue operation)
Time limit: 1 sec

Accepted Answer

Implement a queue using two stacks with enqueue and dequeue operations.

Use two stacks to simulate a queue - one for enqueue and one for dequeue.
For enqueue operation, push elements onto the enqueue stack.
For dequeue operation, if dequeue stack is empty, pop all elements from enqueue stack and push onto dequeue stack.
Return true for successful enqueue and -1 for empty dequeue.
Example: Enqueue 10, enqueue 20, dequeue (returns 10), enqueue 30, dequeue (returns 20).