/*

struct TreeNode {

    int val;

    struct TreeNode *left;

    struct TreeNode *right;

    TreeNode(int x) :

            val(x), left(NULL), right(NULL) {

    }

};*/

class Solution {

public:

    vector<int> PrintFromTopToBottom(TreeNode* root) {

        vector<int> result;

        //申请一个队列专门放横排的数据

        if (root==NULL){

            return result;

        }

        queue<TreeNode*> que;

        que.push(root);

        while(!que.empty()){

            if(root->left!=NULL){

                que.push(root->left);

            }

            if(root->right!=NULL){

                que.push(root->right);

            }

            int val=root->val;

            result.push_back(val);

            que.pop();

            root=que.front();

        }

          return result;

    }

};