从上到下打印二叉树

 1 class Solution {
 2 public:
 3     vector<int> PrintFromTopToBottom(TreeNode* root) {
 4         vector<int> res;
 5         if(root==NULL)return res;
 6         std::queue<TreeNode*> que;
 7         que.push(root);
 8         while(que.size())
 9         {
10             TreeNode *tmp=que.front();
11             que.pop();
12             res.push_back(tmp->val);
13             if(tmp->left)que.push(tmp->left);
14             if(tmp->right)que.push(tmp->right);
15         }
16         return res;
17     }
18 };