Jane Street Interview Questions

Jane Street is a renowned global quantitative trading firm known for blending sophisticated technology, mathematics, and finance. Their hiring practices target individuals with a solid foundation in mathematics, computer science, and statistics, particularly those with extensive experience in algorithm design, data analysis, and financial markets.

In this article, we’ll discuss some tips to prepare for Jane Street interview questions.

Jane Street’s rigorous interview process is designed to identify candidates who can thrive in a fast-paced and intellectually challenging environment. Here’s an overview of the process:

1. Preliminary Discussion

   This first step involves a conversation with a recruiter to learn more about your background, interests, and goals. You might be asked about your academic achievements, past work experiences, and understanding of the trading industry.

2. Quantitative and Problem-Solving Rounds

   Jane Street is known for having challenging quantitative interviews. Expect a series of math and probability questions, brainteasers, and market-related problems. These assessments test your analytical strengths, problem-solving skills, and ability to think on your feet.

3. Technical and Coding Interviews

   Depending on the role, you may have technical interviews to assess your coding and software engineering skills. Be prepared to write code, discuss algorithms, and analyze complex data structures.

4. Onsite Interviews

   The onsite interviews at Jane Street can be a mix of technical, quantitative, and behavioral assessments. You’ll meet with various team members, from traders to researchers, and delve deep into technical topics, trading scenarios, and cultural fit discussions.

Quick Tips for Jane Street Interviews

• Brush up on statistical concepts: Jane Street is known for its tough quantitative questions. Review your math fundamentals, especially statistics and probability.
• Practice coding: If you’re applying for a technical role, make sure your coding skills are sharp by reviewing common algorithms and data structures.
• Understand the trading landscape: Jane Street is at the forefront of quantitative trading. Having at least a basic understanding of financial markets and trading strategies is essential.
• Highlight your interest: Jane Street values intellectual curiosity and integrity. Be genuine in your responses and show a keen interest in learning and growing within the firm.

While databases aren’t the primary focus at Jane Street, understanding them is important to the company’s operations and various financial processes. Some questions to practice with include:

1. How can you find the total cost of all the transactions made per user?

Given transactions, products, and users tables, write a query to calculate the total cost of all transactions per user, ordered by descending order.

The output should include the user’s name, user_id, and the total cost rounded to 2 decimal places.

2. Create a function that can generate a list of coin toss outcomes.

Write a function coin_toss that takes input as the number of tosses and a probability of heads to return a list of randomly generated results equal in length to the number of tosses.

Each result should represent the outcome of a coin toss, where ‘H’ represents heads and ’T’ represents tails.

3. Find each of the products that are priced higher than the cost of the average transaction.

Given two tables, transactions and products, write a query to return the product id, product price, and average transaction total value (price*quantity) of each product with a price greater than the average transaction cost.

To practice Database interview questions, use the SQL learning path or the full list of SQL questions in our database.

Algorithmic thinking is essential for many tech roles. While the core of Jane Street’s operations revolves around finance, having a solid grasp of coding and algorithmic concepts is a significant asset when designing efficient trading strategies and tools.

4. How do you merge two sorted lists?

Given two sorted lists, write a function to merge them into one sorted list.

Bonus: What’s the time complexity?

5. Write a function to find the last node of a singly linked list.

Given a singly linked list, your task is to write a function that finds and returns the last node of the list. If the list is empty, your function should return null.

6. Write a function to sum two numeric strings.

Given two strings, num_str1 and num_str2, write a function to sum the two strings together without directly converting them to integers.

Note: Return the output in string format.

To practice Coding and Algorithms interview questions, try the Python learning path or the full list of Coding and Algorithms questions in our database.

Statistics and probability lie at the heart of financial decision-making at Jane Street. Understanding the nuances of probability allows traders to make informed decisions, mitigate risks, and strategize effectively.

7. What’s the probability of not drawing an Ace from a deck of cards?

Let’s say you have to draw two cards from a shuffled deck, one at a time. Calculate the probability that the second card isn’t an Ace.

8. Calculate the potential budget for a ride-sharing app’s coupon program.

A ride-sharing app that services N riders has a probability p of dispensing a $5 coupon to a rider. What should be the total budget for this initiative?

If a driver picks up two passengers, what’s the probability that both riders get the coupon? What’s the probability that only one of them does?

9. What’s the probability of getting a poker pair from a standard deck of cards?

Let’s say that you’re drawing N cards (without replacement) from a standard 52-card poker deck. Each card is unique and part of 4 different suits and 13 different ranks.

Compute the probability that you will get a pair (two cards of the same rank) from a hand of N cards.

To master Statistics and Probability concepts, work through the Statistics and A/B testing and Probability learning paths. These resources will help you understand and solve complex problems in these areas.

Brain teasers are a major part of Jane Street’s (and any other quant-heavy corporation’s) interview process, reflecting their belief in fostering analytical thinking and problem-solving. These questions test not only mathematical skills but also an individual’s ability to think critically and creatively under pressure.

10. Cafe Infinitea (inspired by Hilbert’s Infinite Hotel)

The Infinite Café has an infinite number of tables, each of which can accommodate one person. Currently, all tables are occupied. Suddenly, an infinite train pulls into the station next door. The train has an infinite number of coaches, and each coach has an infinite number of passengers.

How can the Infinite Café accommodate all the passengers from the train without asking any of the current guests to leave?

Here’s one way to solve it:

1. Start by asking the person at the first table to move to the second table, the person at the second table to move to the fourth table, the person at the third table to move to the sixth table, and so on. Essentially, each person at table number $n$ moves to table number $2n$. This means that all the even-numbered tables will now be occupied, and all the odd-numbered tables will be free.
2. Now, let’s start seating the new guests. We can seat the first passenger from the first coach in the first vacant table (Table 1), the first passenger from the second coach in the third vacant table (Table 3), and so on. In general, the first passenger from coach $n$ is seated at table $2n - 1$.
3. But, we still haven’t seated the other passengers in each coach. To seat them, let’s use the same logic as before. For coach $n$, we’ll ask the first unseated passenger to sit at table $4n$, the second unseated passenger to sit at table $8n$, the third unseated passenger to sit at table $12n$, and so on.
4. If we follow this process, every passenger on the train will have a seat, and every existing cafe customer will keep their seat, but they may move to a different table. Even though the café is infinitely large and was completely full, it still manages to accommodate an infinite train full of an infinite number of passengers!

11. A Cheesy Conundrum

Imagine you have 8 cubes of cheese, all of which look identical. However, one of the cubes is slightly heavier than the others but not enough to notice by just holding it. You have a scale, but you can only use it twice. How can you determine which cube is the heavier one?

Solution:

First, divide the cheese cubes into three groups: two with 3 cubes each and one with 2 cubes. Place the two groups of 3 on the balance scale. If they balance, then the heavier cube is in the group of two. If they don’t, the heavier cube is on the side that tilts the scale.

If the heavier cube is in one of the groups of 3, take that group and choose any two cubes to weigh against each other. If they balance, the cube not on the scale is the heavier one. If they don’t, the heavier cube is on the side that tilts the scale.

If the heavier cube was in the group of two, simply put those two cubes on the scale to find out which one is heavier.

12. Bee-Railed!

Two trains are moving towards each other on the same track. They are initially 100 miles apart. One is moving at 5 mph, and the other at 15 mph. A bee is flying back and forth between the two trains at 25 mph. The bee starts at the same location as the faster train. How far will the bee have flown when the two trains collide?

Solution:

The key to solving this problem is to realize that you don’t need to keep track of the bee moving back and forth. Just figure out how long the trains will take to collide and then see how far the bee can fly in that time. The trains are 100 miles apart and closing in at a combined speed of 20 mph (15 mph + 5 mph), so they will collide in 5 hours (100 miles / 20 mph = 5 hours). The bee is flying at 25 mph, so in 5 hours, it will have flown 125 miles (5 hours * 25 mph = 125 miles).