# Decipher a Code Stick

## Introduction

You're an American spy during the heat of the Cold War and you've managed to intercept a Russian message. Immediately you recognise it as a code stick cipher and wrap it around a pencil. Looking at the paper on the pencil, you don't see anything. Then you try a bigger pencil, and you see it.

## Challenge

You have to write a program that deciphers a code stick. As this is code golf, the shortest program wins.

You may use any English dictionaries for looking up words. Some examples of dictionaries include:

• Querying a text file of words
• Using an inbuilt OS dictionary
• Querying an online dictionary (screen scraping etc.)
• Using an external lib

### All words MUST be valid English words

Each of your pencils has four equally sized faces and are infinitely long. You have five differently sized pencils:

Pencil 1: Shows 1 character on each face
Pencil 2: Shows 2 characters on each face
Pencil 3: Shows 4 characters on each face
Pencil 4: Shows 6 characters on each face
Pencil 5: Shows 8 characters on each face

All ciphers can be deciphered by placing the start of the paper at the top of the pencil and wrapping it down.

## Examples

The following is an example of a cipher:

This can be deciphered by wrapping it around Pencil 2:

Side 1 | Side 2 | Side 3 | Side 4
-------+--------+--------+-------
He     | po     | ge     |  s
ll     | jg     | ha     | ds
o      | bv     | vb     | gh

So now you have four combinations:

Hello , pojgbv, gehavb,  sdsgh

You can now perform a dictionary lookup and see that Hello is the only valid word. Therefore, Hello is the cracked cipher.

Note: Deciphered codes may have spaces in. Example: Hello World

## Test cases

Ciphers can be inputted in any way apart from being hardcoded. The following are a few test cases. You will not be given the pencil size.

boasonespetrabbittonespongomezesray long
lsbvmii derfghthstthasinlomnrtk fg dndthugssawerpoloasefnxafqeormnaqwge padhndi mbavwgam
lipois lisptloopoolsisp lortfippinglthe asse rtedgoodcodeis the best  of enlymoolfangthe  leamingsoulsgodsingering
antidisebd sldkfdw sld sja dmddystablishjzkapxmjhavzlx dld slzbfmentariabahdjdlljagzlxbxlffnd ldnism is hdbsh spjalcpdhstd flcnda very cbd skd alsbfo kfvwfd xlconvolutehs ska ckw dlc fjzlxbckxd word  hs sla k dk skdnlcjcu dk

Any more test cases would be appreciated

### Answers to the test cases

1: astronomy
2: i think therefore i am
3: is lisp the code of the gods
4: antidisestablishmentarianism is a very convoluted word

### Script to generate code stick ciphers:

import string, random, math

word = input('Word:\t')
n = int(input('Pencil:\t'))
pencil = int(-((4*(17*n-77))/((n**4)-(19*n**3)+(136*n**2)-(444*n)+566)))

alpha = string.ascii_lowercase+' '
cipher = ''

side = random.randint(1, 4)
sides =['','','','']

for j in range(len(sides)):
if j+1 == side:
sides[j] = word
if len(word)%pencil != 0:
sides[j] += ' '*(len(word)%pencil)
else:
for k in range(math.ceil(len(word)+(len(word)%pencil))):
sides[j]+=random.choice(alpha)

for l in range(0, math.ceil(len(word)/pencil)*pencil, pencil):
for m in sides:
cipher += m[l:l+pencil]

print('Cipher:\t'+cipher)
print('Side:\t'+str(side))
• Your second test case has at least four perfectly meaningful decryptions. This question is also incomplete in that it says "You can now perform a dictionary lookup" but doesn't provide a dictionary. Aug 28, 2014 at 16:39
• The first example uses Pencil 2, not Pencil 1. Aug 28, 2014 at 21:04
• The new third test case is wrong: the closest candidate decryption to the claimed one is is lisp the codeof the gods (sic). Also it's apparently not clear what the output should be. Am I correct to understand that it should be the (assumed unique) candidate decryption which doesn't contain any non-words? (See comment thread on David Carraher's answer). Aug 29, 2014 at 11:21

# Python - 219178172 175

First crack at it. I'm sure there's room for improvement.

edit1: After suggestions, and copying words file to local file named 'w'
edit2: Fixed a bug where it wasn't using the right number of letters per side. Added 3 chars :(

r=range
s=raw_input()
print[a for a in(''.join(s[m:m+n]for m in r(o*n,len(s),4*n))for o in r(4)for n in(1,2,4,6,8))if not set(a.lower().split())-set(map(str.strip,open('w')))]
• you can save 1 char by removing the space after print, i.e. print[a... Aug 28, 2014 at 20:18
• Defining and using a synonym r=range should save a couple more characters. And similar to the morse code golf question it is shorter to load the dictionary where needed (same for raw_input), even though it might increase the computing time dramatically. Aug 28, 2014 at 20:53
• I don't think I can do the same thing with raw_input due to the fact that I use it in two places, and it loops many times. Aug 28, 2014 at 22:25
• This only works for single word ciphers, not with the other multi-word test cases Sep 20, 2014 at 9:37
• After making sure that my dictionary had all the words (it was missing "gods" and "antidisestablishmentarianism"), this script works properly for all 4 of the test cases. Not sure why you thought it wasn't working, maybe you can explain? Sep 20, 2014 at 14:56

# Mathematica 270 230 251

This now requires that all parsed words be found in a dictionary.

f@q_:=
Module[{c=Characters@q,wd,u=DictionaryLookup},
j@d_:=Union[u@d,u[ToLowerCase@d],WordData@d];
Flatten@Select[Flatten[Table[
StringSplit[""<>Flatten@#]&/@Transpose@ArrayReshape[c,{Round[Length@c/(4 m)],4,m},""],{m,{1,2,4,6,8}}],1],!MemberQ[j/@#,{}]&]]

Test Cases

f["boasonespetrabbittonespongomezesray long"]