题目描述

blablabla

样例

blablabla

算法1

class Solution(object):
    def printFromTopToBottom(self, root):
        """
        :type root: TreeNode
        :rtype: List[List[int]]
        """
        if not root:
            return []
        stack = []
        result = []
        flag = 0
        stack.append(root)
        while stack:
            tmp = []
            for i in range(len(stack)):
                if not flag:
                    cur = stack.pop(0)
                    tmp.append(cur.val)
                    if cur.left:
                        stack.append(cur.left)
                    if cur.right:
                        stack.append(cur.right)
                else:
                    cur = stack.pop()
                    tmp.append(cur.val)
                    if cur.right:
                        stack.insert(0, cur.right)
                    if cur.left:
                        stack.insert(0, cur.left)
            result.append(tmp)
            flag = not flag
        return result