0103.py

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None


class Solution:
    def zigzagLevelOrder(self, root: TreeNode) -> List[List[int]]:
        if not root:
            return []

        ans = []
        deque = collections.deque([root])
        isLeftToRight = True

        while deque:
            currLevel = []
            for i in range(len(deque)):
                if isLeftToRight:
                    node = deque.popleft()
                    currLevel.append(node.val)
                    if node.left:
                        deque.append(node.left)
                    if node.right:
                        deque.append(node.right)
                else:
                    node = deque.pop()
                    currLevel.append(node.val)
                    if node.right:
                        deque.appendleft(node.right)
                    if node.left:
                        deque.appendleft(node.left)
            ans.append(currLevel)
            isLeftToRight = not isLeftToRight

        return ans