Point72 OA Interview Review｜DFA state machine + trading percentile, what is so difficult about quantitative factory questions?

Point72 OA s style has always been very distinct: it is not obsessed with complex dynamic programming (DP) or graph theory puzzles like the tech majors, but is more oriented towards "business logic implementation" and "data processing fundamentals".

The three questions encountered this time, at first glance, are basic questions, but if the usual code is not written enough "oil", it is easy to get stuck in the details of the boundary conditions or custom sorting. The overall experience is: the topic reads very smoothly, but to write bug-free code, you need very solid basic skills.

Interview Overview｜Point72 OA Overall Process and Difficulty Summary

The overall difficulty of this Point72 OA was moderate, but the robustness of the code was required.

Testing process

• Platform: HackerRank / CodeSignal (depending on batch)
• duration: approximately 70-90 minutes (three questions)
• language restriction: Recommended Python / C++ / Java
• difficulty:: Medium (bias towards simulation and statistics)

Core Examination Points:

1. simulation capability: The ability to quickly translate textually described logic (e.g., state machines) into code;
2. Customized Sorting: Multi-conditional sorting is a high-frequency test;
3. statistical thinking: Handles financial data with weights (price x volume).

Question 1: DFA String Validator

Problem.

You are given the definition of a Deterministic Finite Automaton (DFA), which includes.

• A set of states (integers).
• A set of transition rules (e.g., from state A with input char (computing) go to state B).
• A start state.
• A set of accept states.

Your task is to implement a function that takes a string as input and simulates the DFA. Return True if the simulation ends in an "accept state", and False If a transition is not defined for the current state and character, the string is rejected immediately.

Ideas

This question is basic computer science, examining the graph traversal / simulation. Don't be intimidated by the technical term "DFA", which is essentially "walk through a table".

I was doing that:

1. preprocessing: Organize the given transfer rules into a HashMap or a two-dimensional array (lookup table structure), where the Key is (Current State, Input Char)Value is (Next State).
2. analog (device, as opposed digital): Establishment current_state = start_node.
3. iteration (math.): Iterate over each character of the input string to look up the table and update it. current_state.
   • pothole: If you encounter a transfer that doesn't exist in the table (out of the way), it means the input is not legal, and you return it directly False.
4. judgment: At the end of the traversal, check the current_state whether or not accept_states In the assembly.

Summarize: The logic is very straightforward, the focus is on the data structure to choose the right, with Hash Map storage map can do $O(1)$ transfer query.

Question 2: Custom Sort Analysis

Problem.

Given an array of integers, sort the array based on the following custom criteria.

1. Primary Sort Key. Frequency of the integer (Ascending). The numbers that appear fewer times come first.
2. Secondary Sort Key. The integer value itself (Ascending). If two numbers have the same frequency, the smaller number comes first.

Ideas

This question is a typical **Custom Comparator** problem, which is very silky smooth to write in Python, but requires a well-written Comparator if you use C++ or Java.

My solution:

1. statistical frequency: Go through the array first, using a Hash Map (or Python's Counter) Record the number of occurrences of each number.
2. Rewriting Sorting Rules:
   • The sorted Key becomes a Tuple:(frequency, value).
   • Call the language's built-in Sort function directly.

Tips on code implementation:

A sentence of nums.sort(key=lambda x: (count[x], x)) in Python will solve it. This question focuses on your proficiency with the standard library and Lambda expressions, and is a giveaway, but make sure you're quick and precise.

Question 3: Transaction Percentile

Problem.

You are given a list of transaction records, where each record contains a Price and a Volume (number of shares traded at that price). You are also given a target Percentile (e.g., 50th percentile for median).

Find the price at which the cumulative volume exceeds or meets the target percentile of the total transaction volume.

Ideas

This is a very Hedge Fund-esque question.

You can't simply put the prices into an array and take the subscripts, because each price has a different "weight" (volume).

Core logic:

1. arrange in order: The records must first be organized by Price Sort from smallest to largest.
2. Calculated total: Iterate through all the records and calculate the total volume Total_Volume.
3. localization target: Calculate the position of the target ranking Target_Rank = Total_Volume * (Percentile / 100).
4. Prefixes and Scanning:
   • Iterate through the sorted records again, maintaining a Current_Volume_Sum.
   • once (sth. happens, then...) Current_Volume_Sum >= Target_RankThe current price of this record is the answer.

The difficulty with this question is understanding the concept of "weighted median/percentile". It is not about complex algorithms, but about the logic of processing business data.

Point72 OA Frequently Asked Questions FAQ

💬 Q1: Does Python time out because sort slows down?

Generally not. HackerRank is more forgiving of Python's time constraints. As long as you're using the built-in .sort() (Timsort, $O(N \log N)$) instead of handwriting your own bubble sort, performance is perfectly adequate.

💬 Q2: Do I need to deal with floating point precision for the third question?

Usually required. When calculating Target_Rank, pay attention to how the percentage multiplication is rounded (Ceil or Floor), which is usually defined in the description (e.g., "round up"), so be sure to read the question carefully, as a small difference can make a big difference.

💬 Q3: OA Are these the only questions?

The question pool of Point72 is relatively fixed, besides these questions, there are also questions related to string processing and matrix operations. It is recommended to brush up on Array and Hash Map related Medium topics.

💬 Q4: How can I troubleshoot if some Test Cases don't pass?

• first question: Checks if "illegal transfer" is handled (input character is not on the edge of the current state).
• second question: Check that the values are ordered correctly (are they from smallest to largest) when the frequencies are the same.
• third question: Check the percentile calculations when Long Type overflow (if the volume is extremely high) and Target_Rank boundaries (e.g., the case of exactly pressed lines).

Want to take down Point72 / Citadel / Two Sigma and other quantitative factory OA?

Quantitative funds' OA differs from traditional tech firms in that they place a higher value on combining mathematical intuition with data processing.

We at Programhelp have compiled a database of the latest questions from the major Hedge Funds. For OA's like Point72 that favor logic implementation, we offer:

• OA Total Assistance: Coverage of the HackerRank / CodeSignal platform, hidden and secure.
• Voice real-time alert system: Give you real-time hints on critical sorting logic and boundary calculations to guard against Hidden Case pitfalls.
• review of real questions: Take you through the high-frequency question bank of the quantitative factory.

If you are preparing for an interview at Point72 or any other Buy-side company, feel free to contact us to get a solid OA and go straight to the interview!

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