Mix of radix sort and sleep sort. (inspired by @fcamel)

radix_sleep_sort.rb

#!/usr/bin/env ruby

#
# fcamel's implementation in Python: https://gist.github.com/1042867
#

def radix_sleep_sort(numbers)
  max_length = numbers.map {|n| n.to_s.length }.max
  return numbers if max_length.nil?

  (1..max_length).each { |i|

    groups = {}
    numbers.each { |n|
      digit = (n.to_s[-i,1] || '0').to_i
      groups[digit] = [] unless groups.has_key?(digit)
      groups[digit] << n
    }

    sorted_groups = []
    threads = groups.map { |s, g|
        Thread.new {
          sleep(s / 1000.0)
          sorted_groups << g
        }
      }
    threads.each { |t| t.join }

    numbers = sorted_groups.flatten
  }

  return numbers
end

if __FILE__ == $0
  # Usage:
  #
  #   $ ./radix_sleep_sort.rb  23 20 25 512 987 98 5
  #   5
  #   20
  #   23
  #   25
  #   98
  #   512
  #   987

  puts radix_sleep_sort(ARGV.map {|s| s.to_i})
end