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Binary Tree Zigzag Level Order Traversal

Understand how to implement a binary tree zigzag level order traversal by alternating the traversal direction at each level using breadth-first search. This lesson helps you develop skills to efficiently solve common tree traversal problems often featured in coding interviews.

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Statement

Given a binary tree, return its zigzag level order traversal. The zigzag level order traversal corresponds to traversing nodes from left to right for one level, and then right to left for the next level, and so on, reversing direction after every level.

Constraints:

  • The number of nodes in the tree is in the range 00 to 500500.

  • −100≤-100 \leq node.data ≤100\leq 100

Examples

Understand the problem

Let’s take a moment to make sure you’ve correctly understood the problem. The quiz below helps you check if you’re solving the correct problem:

Binary Tree Zigzag Level Order Traversal

1.

What will be the zigzag level order traversal of the following tree?

[0, 2, 4, 1, NULL, 3, -1, 5, 1, NULL, 6, NULL, 8]

A.

[[0], [2, 4] , [1, NULL, 3, -1], [5, 1, NULL, 6, NULL, 8]]

B.

[[0], [4, 2], [1, 3, -1], [8, 6, 1, 5]]

C.

[0, 4, 2, 1, 3, -1, 8, 6, 1, 5]

D.

[NULL]

1 / 2

Figure it out!

Here’s a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Sequence - Vertical
Drag and drop the cards to rearrange them in the correct sequence.
1
2
3
4
5

Try it yourself

Implement your solution in main.py in the following coding playground. You will need the provided supporting code to implement your solution.

Python
usercode > main.py
from collections import deque

from ds_v1.BinaryTree.BinaryTree import TreeNode



# Definition for a binary tree node

# class TreeNode:

#     def __init__(self, data):

#         self.data = data

#         self.left = None

#         self.right = None



def zigzag_level_order(root):



    # Replace this placeholder return statement with your code

    return []
Binary Tree Zigzag Level Order Traversal