(Algorithms in Javascript) Leetcode 15. 3Sum - 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.

leetcode-15-three-sum-to-zero.js

const threeSum = (nums) => {
  let len = nums.length;
  if(len < 3) return [];
  nums.sort(function(a,b){
    return a-b;
  })
  if(nums[0] > 0 || nums[0] + nums[1] + nums[2] > 0) return [];
  if(len === 3) {
    if(nums[0] + nums[1] + nums[2] === 0) return [nums];
    else return [];
  }
  //console.log(nums);
  let result = [];
  let checker = '';
  for(let i=0; i<len-2; i++){
    for(let j=i+1; j<len-1; j++){
      //since the array is sorted, we only need to start from 
      //the last index that where value was found, since 
      //nums[k] has to be a lower number.
      for(let start = len-1, k = start; k>i, k>j;) {
        let triplet = [nums[i], nums[j], nums[k]];
        let tripletString = '/' + nums[i] + ' ' + nums[j] + ' ' + nums[k] + '/';
        if(nums[i] + nums[j] === -nums[k] && !checker.includes(tripletString)){
          result.push(triplet);
          checker += tripletString; 
          start--;
          k = start;
        } else {
          k--;
        }
      }
    }
  }
  return result;
};