Adjacent Repeated Substrings of Arbitrary Length

Question

My buddy was recently asked this interview question and it has me stumped! The question asked him to write a function that would return true if a string had repeated substrings inside of it that were adjacent to each other.

For example, if given:

 String first = "ABCxyABC"; //This string would return false because both "ABC" are not next to each other

 String second = "ABCzzCDE"; //This string would return true because both "z" are next to each other

 String third = "12341234zAE"; // This string returns true as well, as "1234" is repeated and back-to-back

I was thinking that you could use some type of regular expression magic in Java, but that is as far as I could get. Any ideas?

Answer 1

Yes it is quite easy with regex. Simply try to find regex like (.+)\\1
( \\1 is backreference representing match from group 1).

DEMO:

String first  = "ABCxyABC"; 
String second = "ABCzzCDE"; 
String third  = "12341234zAE";

Pattern p = Pattern.compile("(.+)\\1");

System.out.println(p.matcher(first).find());  //false
System.out.println(p.matcher(second).find()); //true
System.out.println(p.matcher(third).find());  //true