First, I attended an interview at a university career fair. There were one HR representative and one technologist; both were nice. After a brief introduction of my resume and strengths, they started asking questions about data structures and algorithms. The questions were not too difficult, but after I provided my solutions, they continuously asked for more detail and how to optimize them. The overall process took around 15 minutes. After the interview, they took my resume and said they would arrange another round shortly.

Design a data structure to store the information of people in a big city, and give reasons.