面试题23 从上往下打印二叉树

题目描述

从上往下打印出二叉树的每个节点，同层节点从左至右打印。

 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         vector<int> v;
14         queue<TreeNode *> q;
15         TreeNode *p = root;
16         while (p || !q.empty()){
17             v.push_back(p->val);
18             if (p->left)
19                 q.push(p->left);
20             if (p->right)
21                 q.push(p->right);
22             if (q.empty())
23                 break;
24             p = q.front();
25             q.pop();
26         }
27         return v;
28     }
29 };