require "digest/sha256"
require "wait_group"

hashes = Set{"1115dd800feaacefdf481f1f9070374a2a81e27880f187396db67958b207cbad",
             "3a7bd3e2360a3d29eea436fcfb7e44c735d117c42d1c1835420b6b9942dd4f1b",
             "74e1bb62f8dabb8125a58852b63bdf6eaef667cb56ac7f7cdba6d7305c50a22f"}
mutex = Mutex.new
wg = WaitGroup.new

('a'..'z').each do |initial|
  wg.add
  spawn do
    pwd = initial + "aaaa"
    while pwd[0] == initial
      hash = Digest::SHA256.hexdigest pwd
      if hash.in? hashes
        mutex.synchronize do
          puts "#{pwd}: #{hash}"
        end
      end
      pwd = pwd.succ
    end
  ensure
    wg.done
  end
end

wg.wait