palindrome regex

palindrome_regexp.rb

def find_longest_palindrome(string)
  string.scan(/
    (?<pair>.){0}
    
    (?<palindrome>
      \g<pair>
        (\g<palindrome>||.)
      \k<pair+1>
    )
  /x).map(&:last).sort_by(&:length).last
end

find_longest_palindrome("abacdfgdcabaypqqpy") # => "ypqqpy"
find_longest_palindrome("abacdfgdcabaypqqpy") == "ypqqpy" # => true