Compare Vietnamese string

compare_vietnamese_string.rb

def string_2array(s)
  s.split('')
end

# return 1 if s2 > s1
# return 0 if s2 == s1
# return -1 if s2 < s1
def my_compare(s1, s2)
  downcase_letters = ' aàáảãạăằắẳẵặâầấẩẫậbcdđeèéẻẽẹêềếểễệfghiìíỉĩịjklmnoòóỏõọôồốổỗộơờớởỡợpqrstuùúủũụưừứửữựvwxyỳýỷỹỵz'.freeze
  upcase_letters = 'AÀÁẢÃẠĂẰẮẲẴẶÂẦẤẨẪẬBCDĐEÈÉẺẼẸÊỀẾỂỄỆFGHIÌÍỈĨỊJKLMNOÒÓỎÕỌÔỒỐỔỖỘƠỜỚỞỠỢPQRSTUÙÚỦŨỤƯỪỨỬỮỰVWXYỲÝỶỸỴZ'.freeze

  hash_chars = {}

  string_2array(downcase_letters + upcase_letters).each_with_index do |char, index|
    hash_chars[char] = index
  end

  longer_string, shorter_string, keep_order = s1.length >= s2.length ? [s1, s2, true] : [s2, s1, false]
  string_2array(longer_string).each_with_index do |char, index|
    if shorter_string[index].nil?
      return keep_order ? -1 : 1
    elsif hash_chars[char] > hash_chars[shorter_string[index]]
      return keep_order ? -1 : 1
    elsif hash_chars[char] < hash_chars[shorter_string[index]]
      return keep_order ? 1 : -1
    end
  end
  0
end

puts my_compare('Lê Công Vinh', 'Nguyễn Công Phượng') # 1
puts my_compare('Nguyễn Công Phượng', 'Lê Công Vinh') # -1
puts my_compare('Lê Công Vinh', 'Lê Công Vinh') # 0
puts my_compare('', 'Lê Công Vinh') # 1
puts my_compare('Lê Công Vinh', '') # -1
puts my_compare('', '') # 0