Visa Inc. Software Developer interview questions

First, I attend the interview in university career fair. There will be one HR and one Technologist, they are all nice. After a brief introduction of your resume and your strength, they started to give me questions about data structures and algorithm. The questions are not too difficult, but after I gave my solution, they continuously ask in detail and how to optimise. The overall process took around 15 minutes. After the interview, they got my resume and said will arrange me another round shortly.