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();
        }
    }
};