Easy Queue Question 34 of 224

How do you implement a queue using two stacks?

DSA interview set · Speak this in 60–90 seconds · Faridabad & Delhi NCR

StackLIFOlast in, first out

QueueFIFOfirst in, first out

Push into an in-stack.

Why interviewers care about Queue:

This is a process

question about Queue.

Panels listen for order,

trade-offs, and what you would actually do on a DSA project - not buzzwords.

Stay structured

Name the idea, why it exists, then one short example.

Close cleanly

End with when you use it and one common pitfall.

Before you speak the answer, walk the interviewer through these steps:

1
Define it
Push into an in-stack.
2
On dequeue, if the
out-stack is empty, pour the in-stack into the out-stack, then pop the out-stack.
3
Each element moves at
most twice, so amortized O(1) per operation with O(n) space.
4
Worst-case dequeue is O(n)
when a pour happens.
5
Common mistake
What juniors usually get wrong.
6
Close
When you pick this over the alternative.

Here's a short line you can speak, broken into clear beats:

Say this line

“Each element moves at most twice, so amortized O(1) per operation with O(n) spac”

Break into beats

Eachelementmovesatmosttwice

Speaking order

2987408337471632900

Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.

Push into an in-stack. On dequeue, if the out-stack is empty, pour the in-stack into the out-stack, then pop the out-stack.