I’ve just finished the Jane Street SDE interview process, and honestly, the psychological pressure was significant.
If you prepare for this company with the mindset of “grinding enough algorithm problems is enough to pass,” it’s very easy to get a wake-up call halfway through.
This is an interview with OA + technology + system design + behavior in all directions at the same time. The difficulty is not in a certain question, but that there is no room for obvious shortcomings.
OA: Run Length Encoding, it's not that the algorithm is difficult, it's whether the thinking is clean.
OA as a whole revolves around Run Length Encoding（RLE） Unfolded, there are three parts in total, and the structure is very neat.
The first two questions：
- encoding
- decoding
The difficulty is more basic, mainly to confirm whether your code is stable and the boundary processing is clear.
The real watershed is in the third question：multiply
The meaning of the title is to “multiply and merge” two RLE-encoded arrays.
The biggest trap here is that you must never decode before encoding.
Many people will subconsciously go this way, but write like this：
- Time complexity directly explodes
- The interviewer can see at a glance that you don't understand the meaning of RLE
The correct idea must be：
- Double pointers advance on two RLE lists
- Consume only the smallest count at a time
- Complete all operations in the "coded state”
The essence of this question is not to test whether you can write code, but to test：
Do you have the engineering thinking to “respect the data structure”?
This is very Jane Street.
Technical aspects / system design: Rate Limiter, continuously asked to the bottom hypothesis
What the system design asks is Rate Limiter, But the interviewer is obviously not satisfied with the standard answer.
The whole process is a process of being disassembled and questioned constantly：
- What to do with a stand-alone machine?
- What's the problem with the fixed window?
- How to maintain the status of the sliding window?
- After multi-instance deployment, where is the status placed?
- How does Redis guarantee atomicity?
- Has Lua script become a bottleneck under high concurrency?
- When the number of users is huge, how to do sharding?
- What to do with the hot key?
- Will the retry request result in repeated deductions? How is idempotence guaranteed?
I can obviously feel that this round is not about ”testing knowledge points", but to see if you have any.：
- Intuition of the real system
- Can you continue to land in the real world under the abstract model?
There are no standard answers to many questions, but youIs the thinking path self-consistent?Very important.
Behavioral: The question of conflict is actually asking “can we work together for a long time?”
Behavioral asks a very common question：
Describe an experience where you had a serious disagreement with your teammates
But Jane Street's point of concern is very clear：
- Will you push the pot
- Will you be stubborn?
- Can you keep communicating rationally under pressure?
What I use is STAR, But the real focus is not on structure, but on the expression of values：
- Use data instead of emotions to convince each other
- Take the initiative to understand each other's goals
- Compromise without affecting the overall result
The essence of this round is to judge：
Are you the one who “can reduce the friction cost of the team”?
A very strong overall feeling
Facing the complete process, my biggest feeling is：
Jane Street does not pursue a certain extreme, but refuses to be obviously short-sighted.
You may not be the fastest person to finish writing the code, but：
- Your code can't be rough
- Your system design can't stop at the conceptual level
- Your BQ can't be like a back template
What they are looking for is the kind of：
People who can keep thinking clearly in complex systems and complex interpersonal environments.
Write at the end
For top companies like Jane Street, the annual recruitment window is extremely short, and a failure almost means that they cannot apply again within two years. Are you sure you want to use your limited experience to challenge such a high-pressure and difficult interview?
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