x.rb

# frozen_string_literal: true
#
# Copyright (c) 2016 Pete Hanson

def number_list_to_string(list)
  list.map(&:to_s).join ''
end

def lowest_number(number_list)
  number_list.permutation
             .map { |list| number_list_to_string(list) }
             .map(&:to_i)
             .min
end

puts lowest_number([23, 550, 1, 80]) # -> 12355080
puts lowest_number([1, 1, 1, 1]) # -> 1111
puts lowest_number([10000, 123, 1890, 11]) # -> 10000111231890