Moderate Two Pointers Question 85 of 224

How do you find all unique triplets that sum to zero?

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

Sort, then for each index i run two pointers on the right side looking for -nums[i], skipping duplicates at all three positions.

WHY — Two Pointers instead of guessing?

Why interviewers care about Two Pointers:

This is a process

question about Two Pointers.

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
Sort, then for each
index i run two pointers on the right side looking for -nums[i], skipping duplicates at all three positions.
2
Sorting is O(n log
n) and the nested scan is O(n^2), extra space O(1) besides the output.
3
Hashing per i is
O(n^2) time with extra O(n) space and more duplicate pain.
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

“Sorting is O(n log n) and the nested scan is O(n^2), extra space O(1) besides th”

Break into beats

SortingisOnlogn

Speaking order

2987408337471632900

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

Key takeaway

Sort, then for each index i run two pointers on the right side looking for -nums[i], skipping duplicates at all three positions. Sorting is O(n log n) and the nested scan is O(n^2), extra space O(1) besides the output.