Binary Tree Level Order Traversal

Given a binary tree, return the level order traversal of its nodes 'values. (ie, from left to right, level by level ).

For example:
Given binary tree{3,9,20,#,#,15,7},

    3   / \  9  20    /  \   15   7

Return its level order traversal:

[  [3],  [9,20],  [15,7]]

Confused what"{1,#,2,3}"Means? > Read more on how binary tree is serialized on OJ.

I haven't practiced it for a long time. I'm a little unfamiliar ~

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    vector
 
   > levelOrder(TreeNode *root)    {        vector
  
    vee;        vector
   
    >ve;        queue
    
      qu;        TreeNode *no;        if(NULL==root)            return ve;        qu.push(root);        int len = qu.size();        while(len!=0)        {            while(len--)            {                no = qu.front();                qu.pop();                vee.push_back(no->val);                if(NULL!=no->left)qu.push(no->left);                if(NULL!=no->right)qu.push(no->right);            }            ve.push_back(vee);            vee.clear();            len = qu.size();        }        return ve;    }};