Design a Distributed Crossword Solver
Company: OpenAI
Role: Software Engineer
Category: System Design
Difficulty: hard
Interview Round: Onsite
Design a distributed solver for crossword-like word puzzles.
You are given a grid containing blocked cells and empty cells, plus a dictionary of valid words. Each contiguous horizontal or vertical run of empty cells is a slot that must be filled with one dictionary word of the same length. Intersecting slots must agree on shared letters.
Your system should support submitting a puzzle, solving it asynchronously, and returning either the first valid solution or all valid solutions. Discuss:
- How to model the search problem.
- How to use DFS with constraint propagation.
- How to distribute the search across many workers.
- How to decide when to split work into more distributed tasks versus letting a worker continue local DFS.
- How to handle fault tolerance when workers crash or become slow.
- How to support early termination once one solution has been found.
Quick Answer: This question evaluates competency in distributed systems design, algorithmic search and constraint satisfaction (e.g., DFS with constraint propagation), workload partitioning, asynchronous processing, and fault tolerance within the System Design domain.