3Sum

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Problem

Given an integer array nums, return all unique triplets [nums[i], nums[j], nums[k]] such that i, j and k are distinct indices and the three values sum to zero. The result must not contain duplicate triplets.

Examples

Example 1

Input:nums = [-1,0,1,2,-1,-4]

Output:[[-1,-1,2],[-1,0,1]]

Example 2

Input:nums = [0,1,1]

Output:[]

No triplet sums to zero.

Constraints

3 <= nums.length <= 3000

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How to approach it: the Two Pointers pattern

Two indices move through a sorted (or sortable) structure — often from opposite ends or at different speeds — to avoid the nested loops a brute-force scan would need.

Look for this pattern when

The input is sorted, or can be sorted without losing information you need.
You're looking for a pair, triplet, or partition that satisfies a sum or comparison condition.
You need to compare values from both ends of a sequence (e.g. palindrome checks).

Read the full Two Pointers guide →

Video walkthroughs

Original problem on LeetCode ↗