given an input string str, return a string such that
- all letters change case
- all digits are replaced with it's compliment to 9 (0 => 9, 1 => 8...)
- each letter is replaced by it's compliment in the alphabet (a => z, B => Y, c => x...)
- the result is reversed
Example:
"abcWXY123" => "678bcdXYZ"
only strings with letters and numbers will be passed in.