LeetCode 77.Combinations

/*LeetCode 077Combinations 递归/回溯题目大意：给两个数n和k,找出1-n这n个数的个数为k的子序列解题思路：递归/回溯参考：http://blog.csdn.net/charles1e/article/details/51646879*/#include <iostream>#include <vector>using std::vector;using std::cout;using std::endl;using std::cin;class Solution {public:    vector<vector<int>> combine(int n, int k)     {        vector<vector<int> > result;        vector<int> path;        DFS(n, k, 1, 0, path, result);        return result;    }private:    //长度为n,要找到长度为k的子序列，起始位置为start,当前个数为cur    //path记录的是一个子序列，result记录的是整个结果    void DFS(int n, int k, int start, int cur, vector<int>& path, vector<vector<int> > &result)    {        if (cur == k)        {//递归出口：path中已经有了k个数            result.push_back(path);            return;        }        for (int i = start; i <= n; ++i)        {            path.push_back(i);            DFS(n, k, i + 1, cur + 1, path, result);    //递归：添加下一个元素            path.pop_back();                            //回溯，弹出当前元素后继续查找        }    }};int main(){    Solution sol;    int n, m;    cin >> n >> m;    vector<vector<int> > result;    result = sol.combine(n, m);    for (auto v : result)    {        for (auto i : v)        {            cout << i << " ";        }        cout << endl;    }    return 0;}/*输入：4 2输出：4 21 21 31 42 32 43 4*/