Palindrome Validator

Question

This code returns true if the sentence is a palindrome, and false otherwise. Is there a better way of doing this?

def palindrome?(sentence)

  array_stripped_sentence = sentence.reverse.downcase.delete('').split('')
  array_stripped_sentence == sentence.downcase.delete(' ').split('')

end 

puts palindrome?("Never odd or even")

Answer 1

You can call reverse on String directly.

While it doesn't particularly apply here, instead of splitting on '', you should use the method chars.

Who says you'll be passing a sentence? Does this method not work for single words? If I call palindrome? 'radar' will I get an error?

I'd recommend using tr to strip out all non-alphabetic characters, instead of just deleteing spaces.

def palindrome?(testing)
  stripped = testing.downcase.tr('^a-z', '')
  stripped.reverse == stripped
end

Answer 2

I am not Ruby developer, so I cannot help you with conventions or if there are short methods.. (It also means that someone aware of these things should edit the answer)

But here is a an improvement which worked for me in online compiler I tried:

def palindrome?(sentence)

  array_stripped_sentence = sentence.downcase.delete(' ').split('')
  array_stripped_sentence == array_stripped_sentence.reverse()

end 

puts palindrome?("Never odd or even")

Main improvement I could see in your code was that you were chaining same methods multiple times, when there was no need.

**

Other improvements:

• What if your string contains characters other Alphanumeric characters and space? For example, Never odd or even! How do you process them? [Hint: Regular expressions]

• If you need to strip away special characters regularly, and not just in palindrome program, it might be better to make a separate function for it.

Answer 3

To get this to work reliably with all the possible whitespace characters, a simple change will suffice:

def palindrome?(sentence)
  letters = sentence.gsub(/[[:space:]]/, '').downcase
  letters == letters.reverse
end

[[:space:]] matches all unicode whitespace, including tabs, returns, non-breaking spaces and other wacky anomolies.

So, for instance, now this works:

puts palindrome?("ÑévëR \u00A0\u2002ødd ør  \tëvéÑ\n\r\t ")  # => true

However, the following won't work, because String#downcase only works with ASCII:

puts palindrome?("ÑévëR ødd ør   \tëvéñ\n\r\t ") # => false

Neither will the following, because the accented chars won't match:

puts palindrome?("Never odd ør   \tëvén\n\r\t ") # => false

If you need to accurately convert accented characters to their root letters, you would need to use something like ActiveSupport's Multibyte Chars.