A binary tree for you, please return it in accordance with the sequence traversal node values, (namely step by step, from left to right to access all the nodes),
Example: binary tree: [3,9,20, null, null, 15, 7],
3
/\
September 20
/\
15 July
Returns to its level traversal results:

[3],
[9],
[15, 7]
]
Now my code output below, what's the problem????????????????
Input,9,20,1,2,3,15 [3]
My code output [[3], [20], [15]]
The expected output should be the result of [[3], [9], [1,2,3,15]]

/* ** Definition for a binary tree node. 
* struct TreeNode {
* int val. 
* TreeNode * left; 
* TreeNode * right; 
* TreeNode (int x) : val (x), left (NULL), right (NULL) {} 
*}; 
*/
The class Solution {
Public: 
Vector LevelOrder (root TreeNode *) {
Vector Re; 
If (root==NULL) 
Return re; 
DequeInt size=1; 
While (size) 
{
Vector Hang; 
TreeNode * temp=the queue in front (); 
Hang the push_back (temp - & gt; Val); 
If (temp - & gt; Left!=NULL) 
The queue. The push_back (temp - & gt; Left); 
If (temp - & gt; Right!=NULL) 
The queue. The push_back (temp - & gt; Right); 
Queue. Pop_front (); 
Size -; 
If (size==0) 
{
Size=queue. The size (); 
Re. The push_back (hang); 
} 
} 
Return re; 
} 
};