【DFS】LeetCode 77. Combinations

LeetCode 77. Combinations

Solution1：我的答案
DFS，时间复杂度 O(n!) O ( n ! ) ，空间复杂度 O(n) O ( n )

class Solution {
public:
    vector<vector<int>> combine(int n, int k) {
        vector<vector<int> > res;
        vector<int> temp;
        my_combine(n, res, temp, 0, k); 
        return res;    
    } 

    void my_combine(int n, 
                    vector<vector<int> >& res,  
                    vector<int>& temp, 
                    int start, int k) { 
        if (temp.size() == k) { 
            res.push_back(temp); 
            return; 
        } else { 
            for (int i = start; i < n; i++) { 
                temp.push_back(i+1); 
                my_combine(n, res, temp, i + 1, k); 
                temp.pop_back(); 
            }
        }
    }
};