15 3Sum.js

// Given an array S of n integers, are there elements a, b, c in S 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.

// For example, given array S = [-1, 0, 1, 2, -1, -4],

// A solution set is:
// [
//   [-1, 0, 1],
//   [-1, -1, 2]
// ]
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/**
 * @param {number[]} nums
 * @return {number[][]}
 */

var threeSum = function(nums) {
  nums.sort((a, b) => a - b);
  const result = [];
  const n = nums.length;

  for (let A = 0; A < n - 2; A++) {
    if (nums[A] > 0) return result;
    if (nums[A] === nums[A - 1]) continue;

    let B = A + 1;
    let C = n - 1;
    while (B < C) {
      const sum = nums[A] + nums[B] + nums[C];
      if (sum < 0) B++;
      else if (sum > 0) C--;
      else {
        result.push([nums[A], nums[B], nums[C]]);
        while (nums[B] === nums[B + 1]) B++;
        while (nums[C] === nums[C - 1]) C--;
        B++;
        C--;
      }
    }
  }
  return result;
};