从上往下打印二叉树

 1 /*
 2 struct TreeNode {
 3     int val;
 4     struct TreeNode *left;
 5     struct TreeNode *right;
 6     TreeNode(int x) :
 7             val(x), left(NULL), right(NULL) {
 8     }
 9 };*/
10 class Solution {
11 public:
12     vector<int> PrintFromTopToBottom(TreeNode *root) {
13         queue <TreeNode *> que;
14         vector<int> res;
15         if(root==NULL)
16             return res; 
17         que.push(root);
18         while(que.size()!=0)
19         {
20             TreeNode *pNode=que.front();
21             que.pop();
22             res.push_back(pNode->val);     
23 
24             if(pNode->left!=NULL)
25                 que.push(pNode->left);
26             if(pNode->right!=NULL)
27                  que.push(pNode->right);
28         }
29         return res;
30     }
31 };