A string is comprised of words defined as continuous runs of alphanumeric characters separated by separators (spaces, commas, periods, semi colons, exclamation marks, any other punctuation symbol except apostrophes').

So a string might look like this :

The hungry scanner keeps a suspicious watch on doctors and their unsuspecting patients

The scanner counts words, collecting those together where a common substring of length 4 or greater occurs.

For example, in the given sentence, suspicious and unsuspecting have a common substring of length 4 "susp". Thus the scanner would output something like this :

 The : 1 hungry: 1 scanner: 1 keeps: 1 a: 1 suspicious, unsuspecting: 2 watch: 1 on: 1 doctors: 1 and: 1 their: 1 patients: 1