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 as:

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

/**
 * 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<vector<int> > levelOrder(TreeNode *root) {
        vector<vector<int>> result;
        if(root==NULL) return result;
        
        vector<TreeNode*> lv;lv.push_back(root);
        while(lv.size()>0)
        {
            vector<TreeNode*> lvnew;
            vector<int> lval;
            for(int i=0;i<lv.size();i++)
            {
                lval.push_back(lv[i]->val);
                if(lv[i]->left!=NULL) lvnew.push_back(lv[i]->left);
                if(lv[i]->right!=NULL) lvnew.push_back(lv[i]->right);
            }
            lv=lvnew;
            result.push_back(lval);
        }
        return result;
    }
};