题目要求:
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], ]代码:
lass Solution { public: vector<vector<int> > ans; vector<vector<int> > combine(int n, int k) { vector<int> tmp; DFS(1, n, k, tmp); return ans; } void DFS(int begin, int n, int k, vector<int>& tmp) { if(begin > n && k != 0)//如果begin超过n但是k有没有到0则返回 return ; if(k == 0)//如果k到了0则已经都选完了 { ans.push_back(tmp); return ; } tmp.push_back(begin); DFS(begin + 1, n, k - 1, tmp);//选择 begin tmp.pop_back(); DFS(begin + 1, n, k, tmp);//不选择begin } };