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Binary Tree Zigzag Level Order Traversal

Question​

What is the most efficient algorithm for traversing a binary tree in a zigzag level order?

Example 1
Input: 
    3
   / \
  9  20
    /  \
   15   7

Output: [[3], [20, 9], [15, 7]]

Solution​

all//Binary Tree Zigzag Level Order Traversal.py
import collections

# 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):
        result = []
        if not root:
            return result
        q = collections.deque([root])
        count = 0
        while q:
            level = []
            for _ in range(len(q)):
                node = q.popleft()
                level.append(node.val)
                if node.left:
                    q.append(node.left)
                if node.right:
                    q.append(node.right)
            if count % 2 == 0:
                result.append(level)
            else:
                result.append(level[::-1])
            count += 1
        return result