Add day 05: MD5 door

Author: petertseng

05_md5_door.rb

@@ -0,0 +1,31 @@
+require 'digest'
+
+real = ARGV.delete('-r')
+input = (!ARGV.empty? && !File.exist?(ARGV.first) ? ARGV.first : ARGF.read).freeze
+zeroes = '00000'.freeze
+
+pass = ''
+pass2 = [nil] * 8
+
+is = 0.step
+if !real
+  # So as not to make Travis run forever:
+  # Indices producing 5 zeroes are precomputed.
+  precomputed_file = "#{__dir__}/hashes/zeroes-#{Digest::SHA256.hexdigest(input)}"
+  is = File.readlines(precomputed_file).map(&:chomp) if File.exist?(precomputed_file)
+end
+
+is.each { |i|
+  md5 = Digest::MD5.hexdigest(input + i.to_s)
+  next unless md5.start_with?(zeroes)
+  puts i if real
+  pass << md5[5]
+  puts pass if pass.size == 8
+
+  pos = Integer(md5[5], 16)
+  if 0 <= pos && pos < 8 && pass2[pos].nil?
+    pass2[pos] = md5[6]
+    break unless pass2.any?(&:nil?)
+  end
+}
+puts pass2.join

README.md

@@ -20,6 +20,9 @@ In general, all solutions can be invoked in both of the following ways:
 Some may additionally support other ways:
 
 * 1 (Manhattan Distance): Pass the entire sequence of instructions as a single argument in ARGV.
+* 5 (MD5 Door): Pass the door ID in ARGV.
+  Due to long running time, by default the indices generating five zeroes have been pre-computed for the default door ID.
+  To redo the computation (necessary if using a different ID), pass the `-r` flag.
 
 # Posting schedule and policy
 

hashes/zeroes-60c394be9f4138c426bac0f80aef6890b84514ef08e07df04e793cb3b6350cc6

@@ -0,0 +1,31 @@
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hashes/zeroes-ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad

@@ -0,0 +1,16 @@
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