# -*- coding: utf-8 -*-

"""

Created on Tue Apr  9 09:33:16 2019

@author: Administrator

层序遍历：从上往下打印出二叉树的每个节点，同层节点从左至右打印。

            1

           /  \

          2    3

         / \  / \

        4  5 6   7

返回列表：[1,2,3,4,5,6,7]

"""

# -*- coding:utf-8 -*-

class TreeNode:

    def __init__(self, x):

        self.val = x

        self.left = None

        self.right = None

class Solution:

    #层序遍历

    def PrintFromTopToBottom(self, root):

        # write code here

        res,result = [],[]

        if root:    #非空节点，若空直接返回空

            res.append(root)    #先将头结点加入其中

            i = 0

            while True:

                if res[i].left:     #如果左节点非空将其加入

                    res.append(res[i].left)

                if res[i].right:    #同理，右节点非空将其加入

                    res.append(res[i].right)

                i += 1

                if i == len(res):   #退出条件是当遍历到列表的长度时候退出

                    break

            for i in res:   #将节点的值加入到列表返回

                if i:   #返回非空节点的值

                    result.append(i.val)

        return result

if __name__ == '__main__':

    solution = Solution()

    node_left = TreeNode(4)

    node_right = TreeNode(5)

    root_left = TreeNode(2)

    root_left.left = node_left

    root_left.right = node_right

    node_left = TreeNode(6)

    node_right = TreeNode(7)

    root_right = TreeNode(3)

    root_right.left = node_left

    root_right.right = node_right

    root = TreeNode(1)

    root.left = root_left

    root.right = root_right

    res = solution.PrintFromTopToBottom(root)

    print(res)