从m个数中取n个数

    void dfs(vector<int> &nums, int m, int k, vector<int> &pick){
        for(int i = m; i >= k; i--){
            pick.push_back(nums[i-1]);
            if(k > 1){
                dfs(nums, i-1, k-1, pick);
            }else{
                ans = min(ans, pick);
            }
            pick.pop_back();
        }
    }

 

    void dfs_(vector<int> &nums, int n, int k, int idx, vector<int> &pick){
        if(k == 0){
            for(auto it : pick) cout << it << " ";
            cout << endl;
            return;
        }
        for(int i = idx; i <= n-k; i++){
            pick.push_back(nums[i]);
            dfs_(nums, n, k-1, i+1, pick);
            pick.pop_back();
        }
    }