leetcode 103. 二叉树的锯齿形层序遍历

用一个变量来标记是否反转

class Solution:
    def zigzagLevelOrder(self, root: TreeNode) -> List[List[int]]:
        if not root:
            return []
        queue = [root]
        ans = []
        flag = True
        while queue:
            temp = []
            for _ in range(len(queue)):
                node = queue.pop(0)
                temp.append(node.val)

                if node.left:
                    queue.append(node.left)
                if node.right:
                    queue.append(node.right)

            if flag:
                ans.append(temp)
            else:
                ans.append(temp[::-1])
            flag = not flag
        return ans