/**
 * 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<int> printFromTopToBottom(TreeNode* root) {
        vector<int>vec;
        if(!root)
            return vec;
        queue<TreeNode *>que_;
        que_.push(root);
        while(!que_.empty())
        {
            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();
            }
        }
        return vec;
    }
};