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;
    }
};