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).

 1 public class Solution { 2     public int threeSumClosest(int[] num, int target) { 3         if (num==null || num.length<3) { 4             return Integer.MIN_VALUE; 5         } 6         int res = num[0] + num[1] + num[2] - target; 7         Arrays.sort(num); 8         for (int i=num.length-1; i>=2; i--) { 9             int cur = twoSum(num, target-num[i], 0, i-1);10             if (Math.abs(cur) < Math.abs(res)) {11                 res = cur;12             }13         }14         return target+res;15     }16     17     public int twoSum(int[] num, int target, int l, int r) {18         int closest = num[l] + num[r] - target;19         while (l < r) {20             if (num[l] + num[r] == target) {21                 return 0;22             }23             int diff = num[l] + num[r] - target;24             if (Math.abs(diff) < Math.abs(closest)) {25                 closest = diff;26             }27             if (num[l] + num[r] > target) {28                 r--;29             }30             else {31                 l++;32             }33         }34         return closest;35     }36 }