regex - How to detect duplicate words from a String in Java?

Question

What are the ways by which duplicate word in a String can be detected?

e.g. "this is a test message for duplicate test" contains one duplicate word test.

Here, the objective is to detect all duplicate words which occur in a String.

Use of regular expression is preferable to achieve the goal.

Answer 1

The best you can do with regexes is O(N^2) search complexity. You can easily achieve O(N) time and space search complexity by splitting the input into words and using a HashSet to detect duplicates.