103. 二叉树的锯齿形层次遍历

https://leetcode-cn.com/problems/binary-tree-zigzag-level-order-traversal/

解法一：层序

设一个布尔变量reverse，初始为False，每层反转一次，根据reverse决定是否将该层数据倒序

import queue
class Solution:
    def zigzagLevelOrder(self, root: TreeNode) -> List[List[int]]:
        if not root:
            return []
        res = []
        q = queue.Queue()
        q.put(root)
        reverse = False    #是否反向，初始为否
        while q.qsize() > 0:
            count = q.qsize()
            data = []
            for _ in range(count):
                node = q.get()
                data.append(node.val)
                if node.left:
                    q.put(node.left)
                if node.right:
                    q.put(node.right)
            if reverse:     #本层反向
                data = data[::-1]
            reverse = not reverse   #置反
            res.append(data)
        return res