How should I practice Binary Tree Zigzag Level Order Traversal?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Microsoft onsite interview problems in FastPrep.

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Binary Tree Zigzag Level Order Traversal

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Problem statement

Given the root of a binary tree, return its values level by level in zigzag order.

Read the root level from left to right, the next level from right to left, and continue alternating directions for every later level.

Function

zigzagLevelOrder(root: TreeNode) → int[][]

Examples

Example 1

root = [3,9,20,null,null,15,7]return = [[3],[20,9],[15,7]]

The second level reverses direction, while the third level returns to left-to-right order.

Example 2

root = [1,2,3,4,null,null,5]return = [[1],[3,2],[4,5]]

Missing children do not create output entries, and direction still alternates by level.

Constraints

The tree is finite and acyclic.
Every node value is a signed integer.