Just finished the interview Duolingo SDE, the biggest feeling is: their interview style is really different from traditional big companies. If you follow the FAANG preparation method and frantically brush LeetCode + memorize system design templates, it may not be fully applicable in Duolingo.
Coding Phone Screen
The phone screen is where two engineers meet together, one is the master and the other is the shadow. The question is not difficult, but quite interesting: give a DataStream Class, you need to judge whether it is a Stack, Queue or PriorityQueue behind it through the behavior of the data flow. The core idea is actually to maintain three structures of simulators in the class and maintain three flags at the same time:
Can_be_stack
Can_be_queue
Can_be_pqEvery time Add() When updating the three structures simultaneously, if the behavior of a certain structure is inconsistent with the data flow, set the corresponding flag to false.Guess() When you decide, you only need to determine which flag is still valid.
Pair Programming
Onsite has a round of pair programming (75 minutes), which gives you a simplified version of the Flask backend project, allowing you to implement a function.
The task I got was: add a Word of the Day API to the homepage. The process is roughly:
- Take a quick look first
ModelsAndRoutes, understand the codebase - Build a simple endpoint and hardcode the return value first
- Add recommendation logic
The simplest implementation is to randomly select a word from the words that the user is learning but has not yet mastered. If you want to be smarter, you can recommend related words based on the topics the user has recently studied.
System Design
The system design question is to design the Learning Streak (number of consecutive learning days).
The basic model is simple:
Current_streak
Last_learning_timestampThe streak is updated when the user completes the course.
But the interviewer will continue to ask some practical questions, such as:
- What to do if users have different time zones
- How to scale when the number of users is large
- How to decouple streak logic
A more reasonable solution is:
- The lesson complete event first enters the message queue
- Streak service asynchronous consumption events
- User streak status exists in Redis
- Scheduled task processing streak reset
The focus is not on complex architectures, but on edge cases and trade-offs.
Behavioral
Duolingo's behavior is actually very important. They pay close attention to why you want to join Duolingo. Answers that get more points usually combine:
- Recognition of the educational mission
- Your own experience using the product
- Understanding of data-driven culture
If you are a user yourself, it will actually be easy to explain.
Stop sticking to LeetCode when using Duolingo!
Sprinting on Duolingo or a similar North American tech company? Stop blindly grinding LeetCode puzzles! This type of company does not consider algorithmic problems, but instead values the essential understanding of data structures, engineering collaboration capabilities and product thinking. There are actually not many interviews about Duolingo online, and the question types and procedures for many rounds are relatively scattered. If you are also preparing for this company, we have compiled a lot of relevant interview experiences and question types here before, including some common inspection points that require real questions and understanding of relevant Interview assistance If so, you can get in touch to discuss.
