算法1

(暴力枚举) $O(n^2)$

blablabla

时间复杂度分析：blablabla

python 代码

Definition for a binary tree node.
class TreeNode(object):
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None
class Solution:
    def printFromTopToBottom(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        if not root:
            return []
        res=[]
        tmp=[root]
        while tmp:
            size=len(tmp)
            row=[]
            for i in tmp:
                row.append(i.val)
            res.extend(row)
            for i in range(size):
                node=tmp.pop(0)
                if node.left:
                    tmp.append(node.left)
                if node.right:
                    tmp.append(node.right)
        return res