Hi PantlessBandit! I'm going to try to explain this since I just got finished looking up how this works.
What chunjef created is known as a regular expression, or regex for short. Regular expressions are a way to describe an analyze string data.
Regular expressions use forward slashes to encapsulate what it is we're looking for in the string.
\w (with a lower case w) means to look for an alphanumeric character
. represents all other characters while * means zero instances
What this means is to leave all the other characters alone like digits.
Finally the 1 means that there should be only 1 instance of each letter.
The i makes the data analysis case insensitive
The ! means NOT
So, to put it all together
Test the string to see if any LETTER (not other characters) does NOT appear more than once.

I hope I explained that right. I just finished learning about it here:
http://eloquentjavascript.net/09_regexp.html#p_uNMQxzr01n

This kata does rely on the indivisibility of bills. If Visya had a cash exchange machine [100, 100, 100] would work because he could put the $100 bills into the cash exchange machine and get back the necessary change.