(Algorithms in Javascript) Leetcode 16. 3Sum Closest - Given an array nums of n integers and an integer target, find three integers in nums such that the sum is closest to target. Return the sum of the three integers. You may assume that each input would have exactly one solution.

leetcode-16-closest-sum-of-3.js

const threeSumClosest = (nums, target) => {
  let len = nums.length, sum=0;
  if(len === 0) return 0;
  if(len <= 3) {
    for(let i=0; i<len; i++){
        sum += nums[i];
    }
    return sum;
  }
  nums.sort(function(a,b){
      return a-b;
  });
  
  let closest = nums[0]+nums[1]+nums[2];
  for(let i=0; i<len; i++){
    for(let j=i+1, k=len-1; j<len-1, j<k; ){
      var sum = nums[i] + nums[j] + nums[k];
      if(sum === target){
          return sum;
      } else if(sum<target){
        if((closest<sum && sum<target) ||
           Math.abs(target-sum)<Math.abs(target-closest)){
            closest = sum;
        }
        j++;
      } else if(sum>target){
        if(closest>sum && sum>target ||
           Math.abs(target-sum) < Math.abs(target-closest)) {
            closest = sum;
        }
        k--; //to reduce sum decrease tail
      }
        
    }
  }
  return closest;
};