291. 3Sum

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

Notice that the solution set must not contain duplicate triplets.

Find all unique triplets in the array which gives the sum of zero. This is a classic two-pointer problem that extends the Two Sum pattern.

Requirements

1. Basic Functionality

• Find all unique triplets that sum to zero
• No duplicate triplets in the result
• Each triplet should be sorted in non-decreasing order

Example Usage

threeSum([-1, 0, 1, 2, -1, -4]);  // [[-1, -1, 2], [-1, 0, 1]]
threeSum([0, 1, 1]);               // []
threeSum([0, 0, 0]);               // [[0, 0, 0]]

Real-World Context

• Financial analysis: Finding combinations of transactions that net to zero
• Chemistry: Balancing equations where components must cancel out
• Game development: Finding balanced team compositions