leetcode 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).

class Solution {/*首先使用三层循环必然是要time limit所以处理数组的时候，首先想到的应该是排序，排序后进行的如果不是二分查找性质的（将复杂度降为logn），就应该前后夹击求和性质（复杂度降为n）。因为在这其中比较好玩的是，需要的不是精确值，而是一个接近值。采用思想为先选择一个，然后剩余值前后夹逼。*/public:    int threeSumClosest(vector<int> &num, int target) {        int len=num.size();    if(len<=2) return 0;    int result;    int min=INT_MAX;    sort(num.begin(),num.end());    for(int i=0;i<len-2;i++){    int temp;    temp=num[i]+sub(num,target-num[i],i+1);    if(abs(temp-target)<min){    min=abs(temp-target);    result=temp;    }    }        return result;    }    int sub(vector<int>&num,int target,int start){int len=num.size();int beg=start,end=len-1;int min=INT_MAX,re;while(beg<end){int temp=num[beg]+num[end];int diff=abs(temp-target);if(diff<min) {min=diff;re=temp;}if(diff==0) return re;if((temp-target)<0) beg++;else if((temp-target)>0) end--;}return re;}};