Pinterest — Machine Learning Engineer ❌ Failed
Level: Unknown Level
Round: Onsite · Type: Multiple Types · Difficulty: 7/10 · Duration: 360 min · Interviewer: Neutral
Topics: Machine Learning, System Design, Behavioral, Dynamic Programming, Trie
Location: San Francisco Bay Area
Interview date: 2025-12-15
Got offer: False
Summary
Round 1: Phone Screen
Question: LeetCode 453.
Round 2: Virtual Onsite - ML Application
Question: Design multiple user embeddings given already trained pin embeddings.
Round 3: Virtual Onsite - ML Design
Question: Design pin home feed ranking.
Round 4: Virtual Onsite - Hiring Manager
Question: Deep dive into my resume.
Round 5: Virtual Onsite - Coding
Question: Given string A, return the minimum number of copies needed to build string B. I am allowed to either copy the whole string A or delete a single letter. Time and space complexity must be optimal.
Round 6: Virtual Onsite - Coding
Question: Implement add, search, and delete operations with optimal time complexity. I didn't finish due to unfamiliarity with Tries.
Details
Preparation Tips & Key Takeaways
What I Learned
- It's crucial to have a strong understanding of fundamental data structures like Tries, especially for roles requiring efficient string manipulation.
- Optimizing time and space complexity is a key expectation, not just for coding rounds, but also for system design.
- Be prepared to discuss past projects in detail during the hiring manager round.
Recommended Preparation
Coding Practice
- Focus on dynamic programming problems for optimization challenges.
- Practice implementing and using Trie data structures.
System Design
- Review common machine learning system design patterns.
- Understand user embedding techniques and ranking algorithms.
Behavioral Questions
- Prepare detailed explanations of projects listed on your resume.
- Practice discussing the challenges and solutions in previous work.
Resources I Recommend
- LeetCode for coding practice.
- System design interview resources focusing on machine learning applications.
Common Pitfalls to Avoid
- Lack of familiarity with essential data structures like Tries.
- Not being able to optimize solutions for both time and space complexity.
- Insufficient preparation for in-depth resume review during the hiring manager round.
LeetCode similar: LeetCode 43