LeetCode--Binary Tree Level Order Traversal

/**
* 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> > res;
if(root == NULL)
{
return res;
}
queue<TreeNode *> q1;
queue<TreeNode *> q2;
q1.push(root);
while(!q1.empty() || !q2.empty())
{
vector<int> tmpres;
if(!q1.empty())
{
while(!q1.empty())
{
TreeNode *tmp = q1.front();
q1.pop();
tmpres.push_back(tmp->val);
if(tmp->left!=NULL)
{
q2.push(tmp->left);
}
if(tmp->right!=NULL)
{
q2.push(tmp->right);
}
}
}
else
{
while(!q2.empty())
{
TreeNode *tmp = q2.front();
q2.pop();
tmpres.push_back(tmp->val);
if(tmp->left!=NULL)
{
q1.push(tmp->left);
}
if(tmp->right!=NULL)
{
q1.push(tmp->right);
}
}
}
res.push_back(tmpres);
}
return res;
}
};