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Applovin·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
May 2026

Summary

Second round at Applovin for a software engineer role. The technical portion was a mini compiler problem paired with a topological sort question, which is a pretty specific combo I wasn't fully expecting.

Questions Asked (1)

Q1

Implement a mini compiler, incorporating topological sort as part of the solution.

Algorithms & Data StructuresTechnical Trade-offs
Author's notes

This one stung a bit.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the scope of the mini compiler (e.g., expression evaluator, dependency resolver, or simple language) and then outline the phases: lexing, parsing, semantic analysis, and code generation. Explain how topological sort fits in—likely for ordering dependencies such as variable declarations, function calls, or instruction scheduling—and then walk through a concrete example.

Pro tip: Mention that topological sort also detects cycles (e.g., circular dependencies), which is crucial for error reporting in compilers; this shows you understand both the algorithm and its practical application.

1. Clarify Requirements

Ask questions to define the compiler's scope: what language features, input/output format, and where topological sort is needed (e.g., dependency graph of symbols or instructions).

2. Design the Compiler Pipeline

Outline the stages: lexer, parser, semantic analyzer, and code generator. Explain how each stage transforms the input and where the dependency graph is built.

3. Integrate Topological Sort

Describe how to construct a directed graph from dependencies (e.g., variable uses, function calls) and apply Kahn's algorithm or DFS to produce a valid order, handling cycles as errors.

4. Walk Through an Example

Use a simple code snippet to illustrate the process: show the dependency graph, the topological order, and how it affects code generation or evaluation.

5. Discuss Trade-offs and Edge Cases

Talk about time/space complexity, cycle detection, and alternatives like lazy evaluation or just-in-time compilation, and how you would test the compiler.

Key Points to Mention

  • Graph representation (adjacency list) and topological sort algorithms (Kahn's vs. DFS)
  • Cycle detection and error handling for circular dependencies
  • Integration with compiler phases: when to build the graph (e.g., during semantic analysis)
  • Complexity analysis: O(V+E) time and space
  • Handling of dynamic dependencies or forward references
  • Testing strategy: unit tests for each phase and integration tests for the whole compiler

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