0103-binary-tree-zigzag-level-order-traversal.py

# Definition for a binary tree node.
# 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 root is None:
            return
        result, zigzagDirection = [], 1
        q = [root]
        while q:
            level, queueLength = [], len(q)
            for i in range(queueLength):
                node = q.pop(0)
                level.append(node.val)
                if node.left:
                    q.append(node.left)
                if node.right:
                    q.append(node.right)
            result.append(level[::zigzagDirection])
            zigzagDirection *= -1
        return result