#103

Binary Tree Zigzag Level Order Traversal

specialist · 655 · lc medium +30 · verified · 63.3% accepted · 11,990 likes · top 66%

Description

Given the root of a binary tree, return its node values collected level by level while alternating the traversal direction: left-to-right for even-numbered levels and right-to-left for odd-numbered levels.

Example 1:

Input: root = [3,9,20,null,null,15,7]

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

Example 2:

Input: root = [1]

Output: [[1]]

Example 3:

Input: root = []

Output: []

Code

# 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]]:

# 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]]: