Citadel Tech Phone Screen for Software Engineer Intern

The interview lasted 45 minutes. The interviewer seemed unfriendly, and I felt a lot of pressure. After scrutinizing my resume, they started asking technical questions. The first question was a simple

The interview lasted 45 minutes. The interviewer seemed unfriendly, and I felt a lot of pressure. After scrutinizing my resume, they started asking technical questions. The first question was a simple staircase problem: calculate the number of different combinations of bricks of length 2 and 3 to form a wall of length n. The number of bricks was unlimited. I answered quickly. The following content requires a score higher than 188. You can already view it. Then they asked how to achieve a faster time complexity than O(n) for a very large n, only needing to calculate the high 8 bits or the low 8 bits. I panicked quickly because I hadn't seen this before. I briefly explained that calculating the high 8 bits could be done using the stirring formula to estimate the major terms and discard the rest. Later, the interviewer suggested using a transition matrix, which could determine the high 8 bits, while the low 8 bits could be calculated using fast exponentiation. The second question asked, "If the probability of any two events A, B, C, and D co-occurring at any given time is 1/4, what are the upper bound and lower bound of the expected number of events occurring at any given time?" I only answered that the lower bound is 1, and for the upper bound, I only mentioned that if they were independent, it would be 2, but that's clearly not the upper bound. Later, due to time constraints, they told me to go back and study algorithms and probability more. I thought I failed, but a week later I was scheduled for another interview (it doesn't seem to be a second interview). Additional content (2025-10-12 11:17 +08:00): Please give me some points!! I'm trying my best to save up points 😭