Easy Sliding Window Question 28 of 224

How do you find the first negative number in every window of size k?

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

PICTURE THIS: DATABASE INDEX

Without indexScan every row

With indexJump to keys

CostWrites slower

Simple meaning

Keep a deque of indices of negatives inside the current window, dropping those that slide out of range.

WHY — Sliding Window instead of guessing?

Why interviewers care about Sliding Window:

This is a process

question about Sliding Window.

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
Keep a deque of
indices of negatives inside the current window, dropping those that slide out of range.
2
The front of the
deque is the first negative, or you report 0 if the deque is empty.
3
Each index enters and
leaves at most once, so time is O(n) with O(k) extra space.
4
Give an example
One tiny concrete case you can say aloud.
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

“The front of the deque is the first negative, or you report 0 if the deque is em”

Break into beats

Thefrontofthedequeis

Speaking order

2987408337471632900

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

Key takeaway

Keep a deque of indices of negatives inside the current window, dropping those that slide out of range. The front of the deque is the first negative, or you report 0 if the deque is empty.