文章作者：Tyan
部落格：noahsnail.com  |  CSDN  |  簡書

1. Description

2. Solution

class Solution {
public:
    vector<vector<int>> combine(int n, int k) {
        vector<vector<int>> result;
        vector<int> combination;
        combine(result, combination, n, k, 1);
        return result;
    }

    void combine(vector<vector<int>>& result, vector<int>& combination, int& n, int& k, int begin) {
        if(n - begin + 1 + combination.size() < k) {
            return;
        }
        if(combination.size() == k) {
            result.push_back(combination);
            return;
        }
        for(int i = begin; i <= n; i++) {
            combination.push_back(i);
            combine(result, combination, n, k, i + 1);
            combination.pop_back();
        }
    }
};
 

Reference

1. https://leetcode.com/problems/combinations/description/