Find all unique triplets summing to zero

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 (i != j != k), and
• nums[i] + nums[j] + nums[k] == 0.

The returned triplets must be unique (i.e., no duplicate triplets in the output). Triplets can be returned in any order.

Input

• nums: an array of integers

Output

• A list/array of unique triplets, each triplet containing three integers whose sum is zero

Constraints (typical interview bounds)

• 0 <= nums.length <= 3000
• -10^5 <= nums[i] <= 10^5

Example

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

Find All Unique Triplets Summing to Zero

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 nums[i] + nums[j] + nums[k] == 0.

To make the output deterministic, return each triplet in non-decreasing order, and return the full list of triplets in lexicographic order. Do not include duplicate triplets.

Hints

1. Sorting the array helps you avoid duplicates and makes it possible to use a two-pointer scan.
2. Fix one number, then look for two remaining numbers whose sum equals its negation.