Leetcode77. Combinations组合

给定两个整数 n 和 k，返回 1 ... n 中所有可能的 k 个数的组合。

示例:

输入: n = 4, k = 2 输出: [ [2,4], [3,4], [2,3], [1,2], [1,3], [1,4], ]

class Solution {
public:
    vector<vector<int> >res;
    int N;
    int K;
    vector<vector<int> > combine(int n, int k)
    {
        if(n == 0 || k > n)
            return res;
        K = k;
        N= n;
        vector<int> v;
        DFS(1, v, 0);
        return res;
    }

    void DFS(int pos, vector<int> &v, int cnt)
    {
        if(cnt == K)
        {
            res.push_back(v);
            return;
        }
        for(int i = pos; i <= N; i++)
        {
            v.push_back(i);
            DFS(i + 1, v, cnt + 1);
            v.pop_back();
        }
    }
};