class Solution { private: vector<vector<int> > ret; vector<int> tmp; public: vector<vector<int> > combine(int n, int k) { ret.clear(); tmp.resize(k); dfs(1,n,k,1); return ret; } protected: void dfs(int dep, int n, int k,int start) { if(dep>k) { ret.push_back(tmp); return; } for(int i=start;i<=n;i++) { tmp[dep⑴]=i; dfs(dep+1,n,k,i+1); } } };