Cloudflare The OA is not easy to deal with in the style of "brushing up", it examines more on engineering understanding, exception handling ability and underlying network knowledge. The OA I got this time contains three coding questions, one debug and a few networking multiple choice questions, which are moderate in intensity but very practical, suitable for students with project/internship experience.
I. Coding Topics
1. Minimal Unique Prefix
You're given a list of non-empty words. For each word, return the shortest unique prefix that distinguishes it from all other words.
Input: ["dog", "cat", "apple", "apricot", "fish"]
Output: ["d", "c", "app", "app", "f"]
Constraints.
- All words are lowercase.
- 1 <= len(word) <= 20
- 1 <= len(words) <= 1000
2. Reverse DNS Mapping
Given a list of hostnames and their IP addresses, build a reverse DNS mapping that shows for each IP address, the list of hostnames mapped to it.
Input: [
("mail.google.com", "8.8.8.8.8"),
("dns.google.com", "8.8.8.8.8"),
("cloudflare.com", "1.1.1.1.1"))
]
Output: {
"8.8.8.8": ["mail.google.com", "dns.google.com"],
"1.1.1.1": ["cloudflare.com"]
}
Notes.
- Hostnames are unique.
- IPs may repeat.
3. Rate Limiter
Implement a basic API rate limiter that restricts how many times a user can make a request within a given time window.
Function Signature.
class RateLimiter.
def __init__(self, limit: int, window: int): ...
...
def allow_request(self, user_id: str, timestamp: int) -> bool.
...
Example.
rl = RateLimiter(limit=2, window=10)
rl.allow_request("alice", 1) # True
rl.allow_request("alice", 2) # True
rl.allow_request("alice", 3) # False (limit reached)
rl.allow_request("alice", 12) # True (outside window)
Common FAQs
Q1: How many questions are there in OA? What are the tests?
3 ways coding (logic + data structure + design)
1 debug (log locating + Python error analysis)
Networking 2 Multiple Choice Questions (TCP/HTTP Basics)
Q2: How difficult are the coding questions? Is there enough time?
The difficulty is moderately practical. The topic itself is not complex, the core is whether you can use clean code to express clear logic. Time is just right, it is recommended to control the rhythm by 20min-20min-25min.
Q3: What is the debug question format?
You will be given a log file of the output of a Python program and asked to point out why the program crashed (e.g. null reference, wrong file path, loop boundary problem, etc.). Actual biased back-end logging troubleshooting question type.
Q4: What is the Networking multiple choice test?
For example:
What layer of the OSI model does DNS belong to?
Which HTTP status code indicates a permanent redirect?
It is recommended to review the TCP/IP 5-layer model + HTTP status codes + common request header fields in advance.
Q5: Do I need to prepare a special environment in advance?
The platform is self-developed, has a clean interface, supports Python3, runs fast, and does not support third-party libraries.
Programhelp Helps you get through OA remotely and securely
Cloudflare is a real-world OA, the test is not about Leetcode questions, but about whether you have real coding experience and whether you can understand the underlying principles of the system. A lot of students get stuck in debugging and networking questions, and they almost get it right, but it's a pity that they end up with a timeout.
Programhelp's Remote Voice Assist service is designed for this type of engineering OA:
Provide reminders for logic sorting and boundary judgment during Coding
Locate core error lines during Debug and quickly analyze logs
Networking provides real-time terminology explanations and selection advice
Full voice accompaniment to ensure "no trace + efficient + accurate".
Find out how we can help you get your hands on an engineering position at Cloudflare / Datadog / Snowflake and more!
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