LeetCode_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) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vector<vector<int>> res;
    	if(root == NULL) return res;
		queue<TreeNode *> myq, myqq;
		myq.push(root);
		while(!myq.empty()){
			vector<int> tp;
			while(!myq.empty()){
				TreeNode* p = myq.front();
				myq.pop();
				tp.push_back(p->val);
				if(p->left != NULL)
					myqq.push(p->left);
				if(p->right != NULL)
					myqq.push(p->right);
			}
			myq.swap(myqq);
			res.push_back(tp);
		}
		return res;
    }
};