/**

 * 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;

        vector<int> path;

        queue<TreeNode*> q;

        if(!root)   return res;

        q.push(root);

        while(!q.empty()){

            int len=q.size();

            while(len--){

                TreeNode* tem=q.front();

                q.pop();

                path.push_back(tem->val);

                if(tem->left!=NULL) q.push(tem->left);

                if(tem->right!=NULL) q.push(tem->right);

            }

            res.push_back(path);

            path.clear();

        }

        return res;

    }

};