Description
https://leetcode.com/problems/binary-tree-zigzag-level-order-traversal/
Given a binary tree, return the zigzag level order traversal of its nodes’ values. (ie, from left to right, then right to left for the next level and alternate between).
For example:
Given binary tree [3,9,20,null,null,15,7]
,
3 / \ 9 20 / \ 15 7
return its zigzag level order traversal as:
[ [3], [20,9], [15,7] ]
Explanation
level order traverse and reverse the result at odd level.
Python Solution
# 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]]:
result = []
if root == None:
return result
queue = []
queue.append(root)
level_index = 0
while len(queue) > 0:
level = []
level_size = len(queue)
for i in range(0, level_size):
node = queue.pop(0)
level.append(node.val)
if node.left:
queue.append(node.left)
if node.right:
queue.append(node.right)
if level_index % 2 != 0:
level = list(reversed(level))
result.append(level)
level_index += 1
return result
- Time complexity: O(N).
- Space complexity: O(N).
One Thought to “LeetCode 103. Binary Tree Zigzag Level Order Traversal”