16.3Sum Closest

3Sum Closest Total Accepted: 34116 Total Submissions: 126585  Question   Solution

Given an array S of n integers, find three integers in Ssuch 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).

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