Moderate Stack Question 95 of 224

How do you implement a MinStack that supports push, pop, top, and getMin in O(1)?

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

PICTURE THIS: STACK VS QUEUE

StackLIFOlast in, first out

QueueFIFOfirst in, first out

Simple meaning

Store values on one stack and running minima on a second stack (or pairs of value and min).

WHY — Stack instead of guessing?

Why interviewers care about Stack:

This is a process

question about Stack.

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.

STEPS — What happens step by step?

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

1
Store values on one
stack and running minima on a second stack (or pairs of value and min).
2
Push updates the min
stack when the new value is <= current min
3
pop the min stack
when the popped value equals that min.
4
All operations are O(1)
time and O(n) space.
5
Common mistake
What juniors usually get wrong.
6
Close
When you pick this over the alternative.

EXAMPLE — See it in action

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

Say this line

“Push updates the min stack when the new value is <= current min”

Break into beats

Pushupdatestheminstackwhen

Speaking order

2987408337471632900

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

Key takeaway

Store values on one stack and running minima on a second stack (or pairs of value and min). Push updates the min stack when the new value is <= current min