← Pinterest Interview Insights
The basic structure came together fine, grant and revoke are just set operations on a per-advertiser collection of group IDs, and check_access walks up the tree comparing ancestors.
Start by clarifying requirements and constraints, then propose a tree data structure with permission propagation. Discuss trade-offs between eager and lazy propagation, and outline operations with time/space complexity. Finally, address scalability and consistency for large hierarchies.
Pro tip: Mention that in real systems like Pinterest, permissions are often cached with TTL and invalidated on updates to balance performance and consistency. Also, consider using a bitmask for permissions to allow efficient checks and updates.
Ask about tree size, update/query frequency, consistency requirements, and whether permissions can be overridden at lower levels. This shows you think about practical constraints.
Propose a tree where each node stores its own permissions and a reference to its parent. Discuss storing effective permissions (propagated) vs. computing on the fly.
For grant/revoke, update the node's permissions and propagate to descendants if eager, or mark dirty if lazy. For check, traverse up to root or use cached effective permissions.
Compare eager vs. lazy propagation: eager gives O(1) checks but O(subtree) updates; lazy gives O(depth) checks but O(1) updates. Discuss hybrid approaches like caching.
Discuss handling large trees with millions of nodes: use efficient traversal, batch updates, and consider distributed caching or sharding. Mention consistency models (e.g., eventual consistency).
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.