leetcode-77. Combinations 组合

Given two integers n and k, return all possible combinations of k numbers out of 1 ... n. Example: Input: n = 4, k = 2 Output: [ [2,4], [3,4], [2,3], [1,2], [1,3], [1,4], ]

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], ]

 思路：dfs

class Solution {
public:
    void dfs(int n,int k,int cur,vector out,vector> & res)
    {
        if(out.size()==k)
        {
            res.push_back(out);
            return;
        }
        for(int i=cur;i<=n;++i)
        {
            out.push_back(i);
            dfs(n,k,i+1,out,res);
            out.pop_back();
        }
    }
    vector> combine(int n, int k) {
        vector> res;
        dfs(n,k,1,{},res);
        return res;
        
    }
};