/**
 * 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>> printFromTopToBottom(TreeNode* root) {
        vector<vector<int>> res {};
        if (!root) return res;

        queue<TreeNode*> q ({root});

        int level = 0;
        for (; !q.empty(); ++level)
        {
            int size = q.size(); 
            vector<int> row {};
            for (int i = 0; i < size; ++i)
            {
                TreeNode *node = q.front(); q.pop();
                if (node->left) q.push(node->left);
                if (node->right) q.push(node->right);
                row.push_back(node->val);
            }
            if (level % 2 != 0) res.emplace_back(vector<int> {row.rbegin(), row.rend()});
            else res.emplace_back(row);
        }
        return res;
    }
};