LeetCode(Combinations)

深搜：

class Solution {public:    vector<vector<int> > combine(int n,int k)     {        vector<vector<int> > result;        vector<int> path;        dfs(n,k,result,path,1,0);        return result;    }    void dfs(int n,int k,vector<vector<int> > &result,vector<int> &path,int start,int step)    {        if(step==k)        {            result.push_back(path);            return;        }        for(int i=start;i<=n-k+1+step;++i)        {            path.push_back(i);            dfs(n,k,result,path,i+1,step+1);            path.pop_back();        }    }};