You can use
a.scan(/(s|k)/).
What’s in between the ‘/ /’ is called a “regular expression”.
These regular expressions are used to find patterns in strings that you
can describe in an approximate way.
They’re a powerful tool.
To see what’s available, look at
_http://www.regular-expressions.info/_
(http://www.regular-expressions.info/)
.
Best regards,
Axel