LeetCode 77 组合

dfs

class Solution {
public:
    vector<int> path;
    vector<vector<int>> res;

    void dfs(int start, int n, int k) {
        if (path.size() == k) {
            res.push_back(path);
            return;
        }

        for (int i = start; i <= n; i ++) {
            path.push_back(i);
            dfs(i + 1, n, k);
            path.pop_back();
        }
    }
    vector<vector<int>> combine(int n, int k) {
        dfs(1, n, k);

        return res;
    }
};