foo.rb

# Reverse letters in string.

def reverse_abstract(list)
  max_distance = (list.length - 1 / 2)
  for i in 0..max_distance do
    left_index  = i
    right_index = list.length - i - 1
    
    left_entry  = list[left_index]
    right_entry = list[right_index]
    
    list[left_index]  = right_entry
    list[right_index] = left_entry
  end
  
  list
end

def reverse(str)
  reverse_abstract(flipped_str)
end

def reverse_words(sentence)
  words = sentence.split ' '
  new_words = reverse_abstract(sentence)
  new_words.join ' '
end

puts reverse('hello')
puts reverse_words('Welcome to the magical world of Iron Man.')