Naive Longest Palindrome

longest_palindrome.rb

# Not the fastest, but working
def longest_palindrome(input_string)
  # default to the first letter, so we return 'a' palindrome if none found
  palindrome = input_string.first
  max = input_string.size

  # Windows over possible substrings and tests for a palindrome
  max.downto(0) do |last|
    0.upto(max) do |first|
      substring = input_string.slice(first..last)
      reversed = substring.reverse
      if substring == reversed && substring.length > palindrome.length
        palindrome = substring
      end
    end

  end

  return palindrome
end

#Simple tests:

longest_palindrome("asdfjfdkljadfabbafjfdldkfhguoenbbhegh")
#> "fabbaf"

longest_palindrome("Brandon Harris")
#> rr

longest_palindrome("nothinginthis")
#> n