Citadel Data Scientist - Low Latency interview questions

The onsite interview lasts for about 6 hours. I spoke to 3 people in the morning and 3 in the afternoon, 20 minutes lunch break. They are quite friendly and some are helpful when you got stuck. The team analyze the data, which traditionally belongs to traders' tasks. This job focuses more on programming rather than building statistical models, not as I expected. The technical problems are quite classic, such as how many loops can you have if connect strings in a bowl, and some C++ concepts. But I did get some weird problems: what is the population in Nigeria? What is its confidence interval? Although the title is data scientist, they did not test much data science related skills, such as machine learning methods. Be prepared to answer advanced questions in both Python (2.x) and C++.