Leetcode Combinations

简单的dfs。

class Solution {public:    vector<vector<int> > combine(int n, int k) {        // IMPORTANT: Please reset any member data you declared, as        // the same Solution instance will be reused for each test case.        ans.clear();        dfs(n, k, 0);        return ans;    }    void dfs(int n, int k, int cnt){        if(cnt == k){            ans.push_back(v);            return ;        }        for(int i = 1; i <= n; i++){            if(v.empty() || i > v[v.size()-1]){                v.push_back(i);                dfs(n, k, cnt+1);                v.pop_back();                }                    }    }    vector<vector<int> > ans;    vector<int> v;};