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#!/usr/bin/env python
from typing import Optional, List
class TreeNode:
def __init__(self, val=0, left=None, right=None):
self.val = val
self.left = left
self.right = right
class Solution:
def zigzagLevelOrder(self, root: Optional[TreeNode]) -> List[List[int]]:
if not root:
return []
res = []
q = [root]
left_to_right = True
while q:
level_size = len(q)
level = []
for i in range(level_size):
node = q.pop(0)
if left_to_right:
level.append(node.val)
else:
level = [node.val] + level
if node.left:
q.append(node.left)
if node.right:
q.append(node.right)
res.append(level)
left_to_right = not left_to_right
return res
if __name__ == "__main__":
solution = Solution()
print(solution.zigzagLevelOrder())
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