/*struct TreeNode {    int val;    struct TreeNode *left;    struct TreeNode *right;    TreeNode(int x) :            val(x), left(NULL), right(NULL) {    }};*/class Solution {public:    vector
    
      PrintFromTopToBottom(TreeNode* root) {        vector
     
       res;        if(root == nullptr) return res;        queue
      
        q;        q.push(root);        while ( !q.empty() ){            auto node = q.front();            res.emplace_back(node->val);            if(node->left != nullptr) q.push(node->left);            if(node->right != nullptr) q.push(node->right);            q.pop();        }        return res;    }};