246.组合总和 III
代码：
class Solution {
public:vector<int> path;vector<vector<int>> finalPath;void backtracking(int index,int sum,int &n,int &k){if(path.size()==k){if(sum==n)finalPath.push_back(path);return;}for(int i=index;i<=9;i++){if(sum+i>n)break;//剪枝操作else{sum+=i;path.push_back(i);backtracking(i+1,sum,n,k);path.pop_back();sum-=i;}}}vector<vector<int>> combinationSum3(int k, int n) {backtracking(1,0,n,k);return finalPath;}
};
