【回溯】16. 3Sum Closest

回溯，当求得三数之和后，更新与target差距最小的和；

class Solution {
public:
    int res=INT_MAX-2;
    int threeSumClosest(vector<int>& nums, int target) {
    	int temp=0;
    	find(nums,temp,target,0,0);
    	return res;
    }
    void find(vector<int>& nums,int temp,int target,int begin,int lenth)
    {
    	if(lenth==3)
    	{
    		res=abs(res-target)<abs(temp-target)?res:temp;
    		return;
    	}

    	for(int i =begin;i<nums.size();i++)
    	{
    		temp+=nums[i];
    		find(nums,temp,target,i+1,lenth+1);
    		temp-=nums[i];
    	}

    }
};