Can you please code it up in Java. If you can use a HashMap/HashSet to solve it that'd be great if not thats okay too.

1. Suppose we have a large text file, and we want to process it in and then be able to answer the following question very quickly for any strings s1 and s2: "How many times does s2 appear immediately after s1 in this text file?" Write a program that reads in a text file and then implements a fast method that we can call repeatedly to answer that question for different strings