Print Folder Path Given Node ID

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[ INFO ] category: Coding difficulty: medium freq: Must first seen: 2026-04-30

[MEDIUM][CODING][MUST]

$ cat problem.md

In this Uber machine coding interview question, you are tasked with finding and returning the full path of a folder given its ID, starting from a "root" folder. 0

Problem Prompt & Constraints

Input: A list of Folder objects. Each folder contains an id, a name, and a list of subfolders (which are the IDs of its child folders).
Root Folder: Defined as any folder with an id of 0. There can be multiple root folders.
Output: A string representing the path from a root to the target node ID (e.g., "rootName" -> "subfolderName" -> "targetName").
Constraints: If no path exists from any root, return an empty string. Nodes can sometimes have multiple parents (forming a directed acyclic graph rather than a simple tree). The printPath method may be called concurrently, so the solution should be thread-safe. All folder IDs except root are typically unique.

Implementation Approach

To solve this efficiently, especially for multiple queries, you should first preprocess the folder list into a parent mapping to allow for fast upward traversal.

1. Preprocess to Map Child to Parent

Create a lookup table (Hash Map) where each key is a child folder ID and the value is its parent's folder ID and name. This allows you to climb "up" from the target node to the root. 3

2. Handle Multiple Roots

Since IDs are unique (except for roots), if you reach a node with ID 0, you have found a valid root and can stop.

3. Trace Path Upward

Starting at the targetID, look up its parent until you reach ID 0. Store the names in a list and reverse them at the end to get the correct order.

user@intervues:~/uber$