3Sum

Given an integer array nums, return all unique triplets [nums[i], nums[j], nums[k]] such that i, j, and k are distinct and nums[i] + nums[j] + nums[k] == 0.

The result must not contain duplicate triplets. You may return the triplets in any order, and the values within each triplet may be in any order. Return an empty list if no such triplet exists.

Constraints:

• 3 <= len(nums) <= 3000
• -10^5 <= nums[i] <= 10^5
• Aim for an O(n²) time solution.

Examples:

• nums = [-1, 0, 1, 2, -1, -4] returns [[-1, -1, 2], [-1, 0, 1]].
• nums = [0, 1, 1] returns [].
• nums = [0, 0, 0] returns [[0, 0, 0]].