When `if` lacks one of the branches `when` and `when-not` are preferred.
Use meaningful names
String is a seq of char. You can avoid that str
You don't need to add seq, seq-like operations do it for you
Instead of searching you can benefit from using sets
Yep, there is a fn for that
Simplify
map, filter & friends are lazy, you better use doseq or doall for IO

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