16. 3Sum Closest

16. 3Sum Closest

Given an array S of n integers, find three integers in S such that the sum is closest to a given number, target. Return the sum of the three integers. You may assume that each input would have exactly one solution.

    For example, given array S = {-1 2 1 -4}, and target = 1.

    The sum that is closest to the target is 2. (-1 + 2 + 1 = 2).

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number}
 */
var threeSumClosest = function(nums, target) {
    
    //几乎和threeSum问题一样，但是这个问题有个好处就是只有唯一解
    var len = nums.length;
    var res = Number.MAX_VALUE;
    var local = Number.MAX_VALUE;
    nums.sort(function(a,b){ return a-b;});
    
    for(var i = 0;i < len;i++){
        
          //转成twoSum 问题
          var temp = target - nums[i];
        
          var left = i + 1; var right = len - 1;
        
         //双指针解法
         while(left < right){
             
              var l = nums[left];
              var r = nums[right];
              var tempsum = l + r;
             
              if(tempsum == temp){                  
                  return target;
              }else if(tempsum < temp){                  
                  left++;      
              }else{
                  right--;
              }
             
             
             if(Math.abs(tempsum+nums[i] - target) < local){
                 
                 local = Math.abs(tempsum+nums[i] - target);
                 res = tempsum+nums[i];
             }
                 
               
           
         }     
        
    }
                 
        return res;
    
};