【leetcode】Combinations

Given two integers n and k, return all possible combinations of k numbers out of 1 ... n.

For example,
If n = 4 and k = 2, a solution is:

[
[2,4],
[3,4],
[2,3],
[1,2],
[1,3],
[1,4],
]

 

类似DFS，采用递归

class Solution {
public:
    static void dfs(int n,int k,int start,int cur,vector<int> &path,vector<vector<int> >&result)
    {
        if(cur==k)
            result.push_back(path);

        for(int i=start;i<=n;i++)
        {
            path.push_back(i);
            dfs(n,k,i+1,cur+1,path,result);
            path.pop_back();
        }
    }
    vector<vector<int> > combine(int n, int k) {
        vector<vector<int> >result;
        vector<int> path;
        dfs(n,k,1,0,path,result);
        return result;
    }
};