102 Binary Tree Level Order Traversal

/**
 * Definition for a binary tree node.
 * 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;
        vector<int> r;
        queue<TreeNode*> tmp;
        tmp.push(root);
        queue<TreeNode*> tmp1;
        while(!tmp.empty())
        {
            r.clear();
            while(!tmp.empty())
            {
                TreeNode* hehe = tmp.front();
                r.push_back(hehe->val);
                if(hehe->left!=NULL)
                    tmp1.push(hehe->left);
                if(hehe->right!=NULL)
                    tmp1.push(hehe->right);
                tmp.pop();
            }
            tmp = tmp1;
            while(!tmp1.empty())
                tmp1.pop();
            res.push_back(r);
        }
        return res;
    }
};