Topological Sort on string

Last updated: September 18, 2025

Quick Overview

Given a directed acyclic graph (DAG) represented as a list of strings, where each string denotes a vertex, implement a function to perform a topological sort on the graph. Your function should return a list of strings representing the vertices in a valid topological order. If the graph contains cycles, return an empty list.

Anthropic
Coding & Algorithms
Machine Learning Engineer
Anthropic
September 18, 2025
Machine Learning Engineer
Onsite
Coding & Algorithms
Medium

105

16

199 solved


Given a directed acyclic graph (DAG) represented as a list of strings, where each string denotes a vertex, implement a function to perform a topological sort on the graph. Your function should return a list of strings representing the vertices in a valid topological order. If the graph contains cycles, return an empty list.

This coding problem is frequently asked during Onsite at Anthropic. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Anthropic expects candidates to write production-quality code, not just solve the puzzle.

What the Interviewer Expects
  • Recognize the underlying problem pattern (sliding window, two pointers, BFS/DFS, etc.)
  • Discuss multiple approaches and trade-offs before coding
  • Implement an optimal solution with clean, production-quality code
  • Handle all edge cases including boundary conditions and invalid input
  • Optimize both time and space complexity with clear justification
  • Test your solution systematically with well-chosen examples
Key Topics to Cover
Data structure selection and trade-offs
Edge cases and input validation
Common algorithm patterns (sliding window, two pointers, BFS/DFS)
Tree structures and recursion
Hash maps and frequency counting
Graph algorithms and traversal
How to Approach This
  1. Clarify input constraints and edge cases before writing code.
  2. Walk through your approach verbally and confirm with the interviewer before coding.
  3. Start with a brute force solution, then optimize. Mention time and space complexity.
  4. Test your solution with examples, including edge cases like empty input or duplicates.
  5. Consider common patterns: sliding window, two pointers, hash map, BFS/DFS, dynamic programming.
Possible Follow-up Questions
  • How would you test this solution thoroughly?
  • How would your solution change if the input was sorted?
  • Can you solve this in a single pass?
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Sample Answer
Problem Analysis

The problem requires us to perform a topological sort on a directed acyclic graph (DAG) represented by a list of strings. This indicates that we can utilize graph traversal algorithms, specifically De...

Approach
  1. Build the Graph: Create an adjacency list from the list of strings, where each string represents a vertex. Initialize an in-degree count for each vertex.
  2. Populate the Graph: For each di...

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