Brute force md5 password crack. Using recursion

pwd_brute_force.rb

require 'digest/sha1'

def combinator(arr, comb_arr = arr, len)
  return if len == 0
  if len == 1
    return comb_arr
  else
    tmp_arr = []
    
    arr.each do |ch|
      comb_arr.each do |comb|
        tmp_arr << comb + ch
      end
    end
    
    combinator(arr, tmp_arr, len - 1)
  end
end

def pwd_brute_force(md5_str, len)
  alphabet = ('a'..'z').to_a
  pwd_combos = combinator(alphabet, len)
  
  pwd_combos.each do |pwd|
    return pwd if Digest::SHA1.hexdigest(pwd) == md5_str
  end
  'Not found'
end
  
md5_str = Digest::SHA1.hexdigest("hey")

puts pwd_brute_force(md5_str, 3)