I remember that when I applied two years ago, the question was still that C++ engineering problem — manually parsing an input string, handling timestamps, and running Kahn's Algorithm to compute a dependency graph. This time the OA was completely different, split into 4 parts. Since you had to keep your camera on, I couldn't take screenshots or photos, so everything below is from memory.
- 10 statistics/probability multiple choice questions
The first 8 were pretty standard. Question 9: What does cross validation reduce?
A. Bias
B. Variance
C. Type I error
D. Type II error
Question 10: I don't remember it well — something about the assumptions behind the F-test / T-test / chi-square test. I had no idea.
- 4 OLS/statistics/portfolio-optimization "boilerplate" questions where you had to show your work
2.1 Doing a linear regression of y ~ a1*x1, where t_1 is the t-stat for a_1 — if you add a new variable x2 that's orthogonal to x1 and redo the OLS, how does t_1 change?
2.2 If a strategy backtests with a Sharpe ratio of 8, but after running it live for k days the return is 0, at what value of k should you start doubting the strategy?
2.3 I forget — also something related to Sharpe ratio, seemed to involve multiple strategies. I didn't have time to look at it closely.
2.4 Suppose random variable X follows an unknown distribution, and we get iid samples x_1, ..., x_n from it. Find the estimator c that minimizes E[|x - c|].
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A C++ numerical computation problem: given a float array arr and a fixed sliding window size k, compute the mean of each sliding window. You had to handle inf, -inf, and nan cases. I didn't even know C++ had that.
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Two medium LeetCode questions
4.1 I forget.
4.2 Given a string, each operation lets you change one character to any character — what's the minimum number of operations so that no two adjacent characters are the same?
I think I probably failed. This OA was pretty tight on time and I didn't remember all the questions — sorry about that, but I hope this still helps.
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