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).

同 3Sum，先排序，后两边夹逼

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class  Solution { public :      int  threeSumClosest(vector< int >& nums,  int  target) {          int  len = nums.size();          if  (len < 3)  return  0;          sort(nums.begin(), nums.end());          int  sum = 0;          int  leastdif = INT_MAX;          for  ( int  i = 0; i < len - 2; i++) {              int  l = i + 1, r = len - 1;                while  (l < r) {                  int  dif =  fabs (nums[i] + nums[l] + nums[r] - target);                  if  (dif < leastdif) {                      leastdif = dif;                      sum = nums[i] + nums[l] + nums[r];                  }                  else  if  (nums[i] + nums[l] + nums[r] < target) {                      l++;                  }                  else  {                      r--;                  }              }          }          return  sum;      } };