/**

 * 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>> v;

        if(root == NULL) return v;

        queue<TreeNode *> q;

        q.push(root);

        TreeNode *curNode = NULL;

        vector<int> a;

        while(!q.empty())

        {

            int len = q.size();

            for(size_t i = ; i < len; i++)

            {

                curNode = q.front(); q.pop();

                a.push_back(curNode->val);

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

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

            }

            v.push_back(a);

            a.clear();

        }

        return v;

    }

};

class Solution

{

public:

    vector<vector<int>> levelOrder(TreeNode* root)

    {

       vector<vector<int>> v;

       levelOrderHelp(root, , v);

       return v;

    }

    void levelOrderHelp(TreeNode *root, int level, vector<vector<int>>& v)

    {

        if(root == NULL) return;

　　　　 // 注意

        if(level >= v.size()) v.push_back(vector<int>());

        v[level].push_back(root->val);

        levelOrderHelp(root->left, level + , v);

        levelOrderHelp(root->right, level + , v);

    }

};