Build User Action Tree | Dataford Interview Questions

Design and implement code to build a user action tree from application logs.

Implement build_action_trees(logs). Each log is a dictionary with id, user_id, action, parent_id, and timestamp. parent_id is None for a root action. Return a dictionary mapping each user ID to a list of root nodes, where each node has id, action, and children. Logs may be unordered; roots and children must be ordered by (timestamp, id). Every non-root parent exists for the same user, and action IDs are globally unique.

Input: logs, a list of dictionaries. Output: a dictionary of nested action trees.

Constraints

0 <= len(logs) <= 10^5
Each log contains id, user_id, action, parent_id, and timestamp
Action IDs are globally unique
parent_id is null for roots
Every non-null parent_id refers to an action for the same user
The action relationships form forests with no cycles
Timestamps and IDs define a deterministic sibling order

Function Signature

def build_action_trees(logs):

Your question is Build User Action Tree. Start with the requirements in the Question tab.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.

Problem

Design and implement code to build a user action tree from application logs.

Input: logs, a list of dictionaries. Output: a dictionary of nested action trees.

Constraints

0 <= len(logs) <= 10^5
Each log contains id, user_id, action, parent_id, and timestamp
Action IDs are globally unique
parent_id is null for roots
Every non-null parent_id refers to an action for the same user
The action relationships form forests with no cycles
Timestamps and IDs define a deterministic sibling order

Function Signature

def build_action_trees(logs):

Your question is Build User Action Tree. Start with the requirements in the Question tab.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.