/**
 * 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:
//1. 队列中存的是这层TreeNode *  while循环 不断访问该层元素存入vector
    vector<vector<int>> printFromTopToBottom(TreeNode* root) {
        vector<vector<int>>res;
        if(!root)
            return res;
        queue<TreeNode *>que_;
        que_.push(root);
        int ceng=0;
        while(!que_.empty())
        {
            ceng++;
            vector<int>vec;
            int num=que_.size();
            while(num--)
            {
                TreeNode *tmp=que_.front(); 
                vec.push_back(tmp->val);
                if(tmp->left)
                    que_.push(tmp->left);
                if(tmp->right)
                    que_.push(tmp->right);
                que_.pop();
            }
            if(ceng%2==0)
                reverse(vec.begin(),vec.end());
            res.push_back(vec);
        }
        return res;
    }
};