Palindrome

palindrome.rb

#!/usr/bin/env ruby

# You can try the running code at http://tpcg.io/FnffuR

# More explicit implementation. The algorithm you described:
# iterating over characters from both ends of string.
# Returning false as soon as first mismatch is found
def palindrome_by_manual_reversing?(word)
  word_string = word.to_s
  # Return early because a word is always a palindrome if
  # it is empty or of length 1
  return true if word_string.to_s.length <= 1
  length = word_string.length
  middle_point = length % 2 == 0 ? length / 2 : (length - 1) / 2
  # Return true if any character from beginning and end doesn't match
  (0...middle_point).any? do |index|
    char_from_start = word_string[index]
    char_from_end = word_string[(length - 1) - index]
    char_from_start == char_from_end
  end
end

# Simpler implementation relying on String#reverse and the fact
# that palindrome reads the same both ways
def palindrome?(word)
  word.to_s == word.to_s.reverse
end

[
  "a",
  "aa",
  "aba",
  "abb",
  "kayak",
  "racecar"
].each { |w| puts "Is '#{w}' a palindrome? #{palindrome?(w)} #{palindrome_by_manual_reversing?(w)}" }

Output:

$ruby main.rb
Is 'a' a palindrome? true true
Is 'aa' a palindrome? true true
Is 'aba' a palindrome? true true
Is 'abb' a palindrome? false false
Is 'kayak' a palindrome? true true
Is 'racecar' a palindrome? true true