SIG (Susquehanna) Interview Questions — Page 5

SIG (Susquehanna)·Software Engineer·Onsite - System Design / Architecture

Jun 2026

Did a system design round at Sig for a software engineer role. The whole thing was one big OOD exercise around a supermarket checkout system, which sounds straightforward until you're actually in it trying to juggle pricing rules, taxes, payments, and receipts all at once.

Design an object-oriented supermarket checkout system. Walk through your class diagram, key abstractions, and how you'd handle items, a shopping cart, pricing rules, taxes, payment methods, and receipt generation.
How would you structure the pricing rules system so that new promotion types (like 'buy 2 get 1 free' or a loyalty discount) can be added without touching existing code?
How would you add a new payment method without breaking the existing payment processing code?

“This is one of those questions that feels manageable at first and then quietly expands on you.”

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SIG (Susquehanna)·Software Engineer·Technical Phone Screen

Jun 2026

SIG quant researcher interview with a probability problem that looks clean on the surface but has a few ways to go sideways if you're not careful about how you set up the distribution.

In a bakery, each customer independently buys a croissant with probability 0.8 or a muffin with probability 0.2. There are only 2 croissants left and 5 customers in line. What is the probability that 2 croissants are enough to cover everyone who wants one?

“So this is basically asking for P(X <= 2) where X is binomial with n=5 and p=0.8.”

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SIG (Susquehanna)·Software Engineer·Technical Phone Screen

Jun 2026

Probability and Bayes' theorem came up hard in this SIG quant interview. One question, clean setup, but the math needs to be airtight or you're done.

30% of posts are fake news. Fake posts have an 80% chance of getting 100+ likes; real posts have an 8% chance. Given a randomly selected post has 100+ likes, what is the probability it's fake news?

“Classic Bayes setup but I fumbled the denominator at first.”

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SIG (Susquehanna)·Software Engineer·Technical Phone Screen

Jun 2026

Sig software engineer interview with a C++ focused technical round. Two scenarios, both designed to look like working code until you actually think about ownership and polymorphism. The kind of stuff that trips you up if you've been writing Python for six months.

You're given a C++ class called Buffer that owns a heap-allocated array via a raw pointer. It has a destructor but no copy constructor or copy assignment operator. Find all the bugs and explain what goes wrong when objects are copied or assigned.
A polymorphic Shape base class and a Circle subclass are stored by value in a std::vector<Shape>. What goes wrong, and how do you fix it?
How does copy-and-swap achieve a strong exception guarantee, and what does it require from swap and the move constructor?
Why is deleting a derived object through a base pointer with a non-virtual destructor undefined behavior?
When would you make Buffer move-only instead of deep-copyable, and how would that change the call sites?

“The double-free is obvious once you see it but I fumbled explaining the rule of three clearly under pressure.”

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SIG (Susquehanna)·Software Engineer·Technical Phone Screen

Jun 2026

SIG quant researcher interview with a physics/math puzzle about balanced mobiles. Pretty niche stuff, felt more like a math olympiad problem than a typical finance interview.

A mobile is structured as a binary tree where each bar splits weight equally between its two sides. If the total weight is 48 lbs and one side keeps branching while the other terminates as a leaf at each level, what is the weight of the leaf hanging at the bottom after 4 levels of halving?

“So basically 48 divided by 2 to the fourth power, which is 3 lbs.”

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SIG (Susquehanna)·Software Engineer·Technical Phone Screen

Jun 2026

SIG quant engineer interview, probability and expected value question. Pretty standard for the firm but the arithmetic can trip you up if you rush.

You roll three fair 6-sided dice. You win $20 if all three match, $10 if exactly two match, and lose $2 if all three are different. What is the expected value per roll?

“I knew the setup immediately but fumbled counting the cases.”

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SIG (Susquehanna)·Software Engineer·Technical Phone Screen

Jun 2026

SIG software engineer interview that went deep into string matching and data structures. One meaty problem about extracting stock tickers from news headlines, with a lot of follow-up on scaling and dictionary updates. Felt more like a system design slash algorithms hybrid than a pure coding round.

Given a stream of news headlines and a dictionary mapping stock tickers to their aliases (e.g., 'AAPL', 'Apple', 'Apple Inc.'), how would you extract the set of tickers mentioned in each headline? Your solution needs to handle case-insensitive matching, whole-word boundaries, multi-word aliases, and deduplication when both a ticker and its alias appear in the same headline.
How would you design the data structures to support fast multi-pattern matching across a large alias dictionary, and how would you handle live updates to that dictionary?

“This one had a lot of layers and I kept peeling them back in the wrong order.”

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SIG (Susquehanna)·Software Engineer·Technical Phone Screen

Jun 2026

Interviewed for a quant researcher role at SIG and got hit with a classic logic puzzle. Short and focused, just the one problem but it required clean reasoning under pressure.

On an island where knights always tell the truth and knaves always lie, person A says 'we are both the same type' and person B says 'we are each a different type.' What type is each person?

“The key thing I noticed pretty fast is that A and B are directly contradicting each other, so exactly one of them is telling the truth.”

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SIG (Susquehanna)·Software Engineer·Technical Phone Screen

Jun 2026

SIG quant engineer interview with a probability/integration problem that felt more like a math exam than a conversation. One question, pretty involved setup, and you're expected to just go.

A person wants to catch a bus to a cinema in time for a movie. Given a probability distribution for bus arrival times and known travel time, what is the probability they make it before the movie starts? Set up the distributions and solve via integration.

“This one required actually writing out the math, not just describing it.”

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SIG (Susquehanna)·Software Engineer·Technical Phone Screen

Jun 2026

SIG quant researcher interview with a probability geometry problem. Pretty classic overlap question but the setup trips you up if you're not careful about how you model continuous uniform distributions.

A purple flower starts blooming at a uniformly random time in a 10-day window and stays in bloom for 4 days. Independently, a red flower starts blooming at a uniformly random time in the same 10-day window and stays for 2 days. What is the probability that both flowers are in bloom at the same time?

“I set up the sample space as a 10x10 square where each axis is the start time of one flower, then figured out which region of that square leads to overlap.”

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