Airtable·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

Apr 2026

Summary

Airtable software engineer interview that was basically one meaty design question about building an undo/redo system. Not a typical leetcode grind, which I appreciated, but the depth they expected on edge cases caught me a bit off guard.

Questions Asked (1)

Design and implement an undo/redo system. Walk through the data structures, the core operations, and any edge cases or invariants you'd need to handle.

Algorithms & Data StructuresSystem DesignTechnical Trade-offs

Author's notes

I jumped straight to two stacks and felt pretty good about it.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements (e.g., single-user vs collaborative, memory constraints, command granularity) and then propose a command pattern with two stacks (undo and redo). Walk through the core operations (execute, undo, redo) and discuss edge cases like stack overflow, branching, and memory management.

Pro tip: Demonstrate awareness of Airtable's collaborative environment by mentioning how undo/redo would work in a multi-user setting, such as using operational transforms or CRDTs, and how to handle conflicts.

1. Clarify Requirements and Constraints

Ask about the scope: single-user or collaborative? What operations need undo/redo? Are there memory limits? This ensures the design meets the actual needs.

2. Choose Data Structures

Propose using two stacks (undo and redo) to store commands or state snapshots. Discuss trade-offs between storing full snapshots vs. deltas/commands.

3. Define Core Operations

Outline execute, undo, and redo methods. Explain how they manipulate the stacks and maintain invariants (e.g., redo stack cleared on new action).

4. Handle Edge Cases and Invariants

Address scenarios like empty stacks, stack overflow (limit size), branching (new action after undo), and memory management (e.g., using a circular buffer or compression).

5. Discuss Extensions and Trade-offs

Mention advanced topics like grouping commands, persistence, and collaborative undo/redo. Highlight trade-offs between simplicity and functionality.

Key Points to Mention

Command pattern: encapsulate actions as objects with execute and undo methods.
Two stacks: undo stack for executed commands, redo stack for undone commands.
Invariant: redo stack is cleared when a new command is executed after undo.
Memory management: limit stack size, use compression, or store deltas instead of full state.
Edge cases: undo/redo on empty stacks, branching, and handling non-undoable actions.
Collaborative context: use operational transforms or CRDTs for multi-user undo/redo.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.