3Sum.js

/*
3Sum
https://leetcode.com/problems/3sum/description/

Given an array nums of n integers, are there elements a, b, c in nums such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.

Note:

The solution set must not contain duplicate triplets.

Example:

Given array nums = [-1, 0, 1, 2, -1, -4],

A solution set is:
[
  [-1, 0, 1],
  [-1, -1, 2]
]
*/

/**
 * @param {number[]} nums
 * @return {number[][]}
 */
var threeSum = function (nums) {
  var ret = [];
  nums.sort(function (a, b) {
    return a - b;
  });
  for (var i = 0; i < nums.length; i++) {
    if (i === 0 || (i > 0 && nums[i] !== nums[i - 1])) {
      var left = i + 1;
      var right = nums.length - 1;
      while (left < right) {
        const sum = nums[left] + nums[right] + nums[i];
        if ((left > i + 1 && nums[left] === nums[left - 1]) || sum < 0) {
          left++;
        } else if (
          (right < nums.length - 1 && nums[right] === nums[right + 1]) ||
          sum > 0
        ) {
          right--;
        } else if (sum === 0) {
          ret.push([nums[left], nums[right], nums[i]]);
          left++;
          right--;
        }
      }
    }
  }

  return ret;
};

module.exports.threeSum = threeSum;