剑指offer 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*> node;
14         vector<int> list;
15         if( root == NULL ) return list;
16         node.push( root );
17         //判断队列中元素是否为空，为空即已将全部子节点遍历完毕
18         while( !node.empty() ){
19             list.push_back( root->val );
20             if(root->left != NULL)
21                 node.push(root->left);
22             if(root->right != NULL)
23                 node.push(root->right);
24             node.pop();
25             root = node.front(); //让当前节点指针root 指向队首元素
26         }
27         return list;
28     }
29 };