Function threeSum

arrays/three-num-sum.js:40–74

(nums)

// Time O(n^2)
// Space O(n)
var threeSum = function (nums) {
  nums.sort((a, b) => a - b);
  let triplets = [];

  for (let i = 0; i < nums.length - 2; i++) {
    if (i > 0 && nums[i] == nums[i - 1]) continue; //avoid duplicates

    let leftPointer = i + 1;
    let rightPointer = nums.length - 1;

    while (leftPointer < rightPointer) {
      let currentSum = nums[i] + nums[leftPointer] + nums[rightPointer];
      if (currentSum === 0) {
        triplets.push([nums[i], nums[leftPointer], nums[rightPointer]]);
        leftPointer++;
        rightPointer--;
        while (
          leftPointer < rightPointer &&
          nums[leftPointer] == nums[leftPointer - 1]
        )
          leftPointer++; //avoid duplicates
        while (
          leftPointer < rightPointer &&
          nums[rightPointer] == nums[rightPointer + 1]
        )
          rightPointer--; //avoid duplicates
      } else if (currentSum > 0) {
        rightPointer--;
      } else if (currentSum < 0) {
        leftPointer++;
      }
    }
  }
  return triplets;
};