DSA · Trees & BFS · #46
Binary Tree Zigzag Level Order Traversal
Module 49 · difficulty 3/5·⏱ 30:00starts on first keystroke
Given the `root` of a binary tree, return the **zigzag level order traversal** of its nodes' values. (i.e. from left to right, then right to left for the next level, and alternate between). Each tree node is `{ val, left, right }`, where `left`/`right` are child nodes or `null`. Implement `function zigzagLevelOrder(root)` that returns an array of arrays, one inner array per tree level (top to bottom).
Examples
root = [3,9,20,null,null,15,7]→[[3],[20,9],[15,7]]— Level 0 left-to-right; level 1 right-to-left; level 2 left-to-right.root = [1]→[[1]]root = []→[]— Empty tree yields an empty result.
Constraints
- · The number of nodes in the tree is in the range [0, 2000].
- · -100 <= Node.val <= 100
Session phases
A · Clarify
B · Approach
C · Complexity
D · Edges
E · Code
F · Tradeoff
G · Score
Phase A — Clarify
Ask questions about input bounds, types, and edge constraints.
Ask the coach clarifying questions about the problem.
When you've covered this phase, advance to the next.