Flatten Nested Comments
Company: Nextdoor
Role: iOS Engineer
Category: Coding & Algorithms
Difficulty: easy
Interview Round: Technical Screen
You are given a list of top-level posts, where each post may contain a list of nested comments, and each comment may itself contain more nested replies.
Write a function that flattens this hierarchical discussion structure into a single array in depth-first order.
Each node has the form:
- `id`: unique identifier
- `content`: text
- `children`: array of child comments
Example input:
- Post A
- Comment A1
- Reply A1a
- Comment A2
- Post B
A valid flattened output in DFS order would be:
`[Post A, Comment A1, Reply A1a, Comment A2, Post B]`
Follow-up 1: Modify the function so it only flattens nodes up to a given maximum depth. For example, if `maxDepth = 1`, include the root posts and their direct children, but do not include deeper replies.
Follow-up 2: Implement the same flattening logic iteratively using a loop instead of recursion.
Quick Answer: This question evaluates proficiency with tree traversal and hierarchical data manipulation, specifically recursion versus iterative approaches and enforcing depth limits when flattening nested structures.