# Python Interview with a Google engineer

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### Interview Summary

**Problem type**  
Rate Limiter

**Interview question**  
Whenever you expose a web service/api endpoint, you need to implement a rate limiter to prevent abuse of the service (DOS attacks).

Implement a RateLimiter Class with an isAllowed() method. Every request comes in with a unique clientID. Deny a request if that client has made more than N successful requests in the past T milliseconds.

**Example:**  
Input:  
N=2, T=100

Requests (c is client id, t is timestamp):  
c=1, t=1  
c=1, t=50  
c=1, t=100  
c=1, t=150  
c=1, t=199  
c=1, t=200

### Interview Feedback

**Feedback about The Legendary Waffle (the interviewee)**  
Advance this person to the next round?  
Yes

- **Technical skills:**  
4/4
- **Problem-solving ability:**  
4/4
- **Communication ability:**  
4/4

> \+ Algorithms & DS (Outstanding):  
> \* Came up with optimal solution within minutes.  
> \* Correctly figures out space and time complexity.  
> \* Initially up with sub-optimal datastructure but quickly realizes than list could have been a queue for O(1) deletion. Solid improvement.  
> \- Couldn't come up with solid solution for the followup.  
>  
> \+ Programming (Solid):  
> \* Checks on edge cases such as bad input.  
> \* Clean code, nice handling of edge cases.  
> \- During implementation time complexity changes to O(N), doesn't notice while can be if for O(1) complexity.  
> \* Nice debugging skills, walk through the code.  
> \* Mentions concurrency for multiple client handling.  
> \* Mentions exception for error handling.  
> \- Struggled a bit on implementation of followup.  
>  
> \+ Values Feedback (Outstanding):  
> \* When pointed about complexity, comes up with better solution of O(log(N)).  
> \* When hinted toward production traffic, thinks about concurrency.  
>  
> \+ Communication (Outstanding):  
> \* Excellent communication, overall kept it casual and easy.

**Overall:**  
Strong Hire at L3. Learning Hire at L4.  
TC absolutely crushed the interview. Great job across all rubrics. I have no reservation in recommending a hire for them at L3.

**Feedback about Doctor Squab (the interviewer)**  
Would you want to work with this person?  
Yes

- **How excited would you be to work with them?**  
4/4
- **How good were the questions?**  
4/4
- **How helpful was your interviewer in guiding you to the solution(s)?**  
4/4

> It felt like you were pushing my solution to be better throughout the interview through the follow-up questions, which I really appreciated. I also appreciated that the question was more practical, and less of a "trick" LeetCode question. The feedback at the end was very helpful as well! Thanks for your time today.

### Interview Transcript

**Doctor Squab:** Yeah. Okay, I usually start with introduction and please feel free to introduce as much or as little you would like. Yeah, I left Google recently. I was a staff engineer there...

**The Legendary Waffle:** Sure. So I'm a software engineer with about three years of experience...

**Doctor Squab:** Yeah, since you're targeting Google, it would be nice to very quickly go over the Google rubric of coding interviews and what they're looking for...

> ... maintain a priority queue with a pointer, to the original queue...