题目

combinations

算法

* 直接模拟

代码

* 直接模拟

class Solution {

public:

    vector<vector<int> > combine(int n, int k) {

        vector<vector<int> > res;

        vector<int> out;

        combineDFS(n, k, 1, out, res);

        return res;

    }

    void combineDFS(int n, int k, int level, vector<int> &out, vector<vector<int> > &res) {

        if (out.size() == k) res.push_back(out);

        else {

            for (int i = level; i <= n; ++i) {

                out.push_back(i);

                combineDFS(n, k, i + 1, out, res);

                out.pop_back();

            }

        }

    }

};