Advent of code, day 4

day4.rb

#!/usr/bin/env ruby

require "digest/md5"

# http://adventofcode.com/day/4

INPUT = "yzbqklnj"

def find(regex)
  loop.with_index do |_, i|
    plaintext = "#{INPUT}#{i}"
    hash = Digest::MD5.hexdigest(plaintext)
    return i if hash =~ regex
  end
end

puts find(/^0{5}/) # part 1
puts find(/^0{6}/) # part 2