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.

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).

排序后固定一个数，两边夹逼另外两个数

class Solution {public:    int threeSumClosest(vector<int> &num, int target) {        int gap=INT_MAX;        sort(num.begin(),num.end());        for(int i=0;i<num.size();i++){            int j=i+1,k=num.size()-1;            while(j<k){                int sum=num[i]+num[j]+num[k];                if(abs(sum-target)<abs(gap)) gap=sum-target;                if(sum-target>0) k--;                else if(sum-target<0) j++;                else return gap+target;            }        }        return gap+target;    }};