Rakuten Kobo interview questions

I was sent coding questions by email. It was supposed to be done within 2 hours, but I could use more than that. Coding questions: Q1. Write an application that can convert a product ID number to a standard ISBN-10 number. I was sent a document that describes the algorithm used to convert a product id into ISBN-10. So, using whatever there is in the document, I wrote the algorithm in Java. Q2. Given an array of arbitrary length that is fully populated with randomly distributed int values: 1, 2, and 3, write the most efficient algorithm you can think of that sorts the array into ascending int order. This is easy. Q3. This question was an un structured way of working with data. The candidate has to improve the code and logic. So basically I wrote classes to make the application object oriented. After sending them the solutions, I was contacted the next day for an interview at Kobo office. They went through the solutions and commented on it and asked how some of the codes could be improved. I was up against 4 people; team lead, architect, product manager and R&D director the same day. They asked easy technical and behavioral questions.