Having just recently experienced Perplexity The two rounds of interviews for Staff Software Engineer were very fast paced and focused. The overall feeling is that it is more inclined to the comprehensive examination of practical logic and efficient communication skills. While my memory is still fresh, I would like to review the interview process and preparation tips in detail.
Round 1: Coding + System Design (90 min)
Coding Scenario Question: Rental Car API
Title Description
Given a longitude respond in singing latitude, if returned in the premium region trueOtherwise, return false.
Requires the implementation of a function:
- If the current coordinates are inside the premium area, return a path that gets out of the premium area
- Otherwise, a coordinate point outside the premium area is returned
This question is more concerned with whether the ideas make sense and the logic is clear, rather than whether the code runs straight through.
My thought process at the time was as follows:
- Defining premium areas: can be abstracted into a polygon or a circle.
- Determine if the current point is in the region: Determine whether a point is inside a polygon using the algorithm "Is a point inside a polygon?".
- route planning: Expand outward from the current point (either by BFS or greedy) until you find a point that is not in the premium region.
- come (or go) back: Once the boundary is found, the corresponding path or coordinates are returned.
Interviewers look for the following more than anything else:
- How do you dismantle the problem;
- Whether to consider boundary cases (e.g., points on the boundary, multiple premium areas overlapping, etc.);
- Robustness to API design, e.g. rate limit, anti-scraping, anti-forgery requests, etc.
System Design Component: Preventing Fraud and API Misuse
Next they extended to the system level and asked how to prevent abuse if this API goes live.
I mentioned a few key points:
- Rate limiting: Limit the invocation frequency for each IP or token;
- API Key and authentication mechanism: control access rights;
- Abnormal traffic monitoring: identify bots or bulk requests;
- Geo Data Cache: Caches geo query results to minimize double counting.
They also asked about how to handle large-scale queries. I added:
- Layered architecture design (load balancing, service splitting);
- Use a CDN or edge caching;
- Hot and cold data hierarchies with asynchronous update mechanisms.
The overall process is very hands-on, focusing not on the eight strands, but on the ability to use logic to build a secure, scalable system.
Second round: Hiring Manager behavioral interview (45 min)
This round had no coding at all, it was all behavioral questions. It was fast-paced, but the questions were classic, focusing on leadership, communication and project control. I used the STAR (Situation-Task-Action-Result) method to answer them.
"How did you resolve cross-team collaboration challenges?"
I spoke about a project that was responsible for cross-team collaboration:
- Situation: Inconsistency of goals and lack of synchronization of information between teams;
- Task: As the primary interface, need to align timelines with delivery targets;
- Action: Proactive organization of alignment meetings with clear division of labour and nodes for regular follow-up;
- Result: The project was completed ahead of schedule and cooperation was smooth.
The interviewer will mainly look for your ability to proactively identify problems and resolve conflicts through communication.
"Give an example of making an unpopular decision."
I shared a case study about the choice of technology route. At the time, I insisted on a more stable but slower iterating option:
- rationale: The team has limited resources and stability is more important than speed;
- act: Support choices with data and risk assessment results;
- in the end: This decision has proved to be a significant reduction in late maintenance costs.
The point of this question is to show how you communicate and persevere, rather than emphasizing "I'm right."
"How did you handle requirement changes?"
I described a scenario where the requirements change:
- Situation: Two weeks before launch, the product suddenly changed its core logic;
- Action: First to assess impact, reschedule and communicate adjustments to relevant parties;
- Result: Although delayed by a week, the overall risk was manageable and the project went live smoothly.
It is recommended that you prepare for this kind of question by choosing more cases related to cross-team collaboration and scope changes.
Interview Preparation Summary
The whole interview gave me the impression that they valued the candidate's practical skills and communication logic.
- Coding doesn't have to be bug-free, but your ability to analyze and disassemble problems must be solid;
- The system design should be down to practical details such as security, abuse protection, and performance;
- Behavioral questions should be sincere and specific and avoid reading from a book.
Not everyone can make it through an interview, but they have "hang-ups."
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