leetcode[16]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 {
public:
    int threeSumClosest(vector<int> &num, int target) {
        if(num.size()<3)return 0;
        sort(num.begin(),num.end());
        int j,k;
        int res=num[0]+num[1]+num[2];
        for(int i=0;i<num.size();i++)
        {
            j=i+1;
            k=num.size()-1;
            while(j<k)
            {
                int sum=num[i]+num[j]+num[k];
                res=(abs(sum-target)<abs(res-target))?sum:res;
                if(sum<target)j++;
                else if(sum>target)k--;
                else return target;
            }
        }
        return res;
    }
};