I have loads of different ciphers stored in a document I once compiled as a kid, I picked a few of the ones I thought were best suitable for challenges (not too trivial, and not too hard) and transformed them into challenges. Most of them are still in the sandbox, and I'm not sure yet whether I'll post all of them, or only a few. Here is the third and easiest one (after the Computer Cipher and Trifid Cipher I posted earlier).

With a Clock Cipher we use the following image to encipher text:

enter image description here
So a sentence like this is a clock cipher would become:

t  h i s     i s     a     c l  o  c k     c i p  h e r    (without additional spaces of course, but added as clarification)


Given a string sentence_to_encipher, encipher it as described above.

Challenge rules:

  • You can assume the sentence_to_encipher will only contain letters and spaces.
  • You can use either full lowercase or full uppercase (please state which one you've used in your answer).
  • You are not allowed to add leading zeros for the single-digit enciphered letters b through j, but two zeros 00 are mandatory for spaces.
  • You should use : as separator, and an additional leading or trailing : is not allowed.
  • You are allowed to use lowercase am and pm instead of uppercase AM and PM, as long as it's consistent.

General rules:

  • This is , so shortest answer in bytes wins.
    Don't let code-golf languages discourage you from posting answers with non-codegolfing languages. Try to come up with an as short as possible answer for 'any' programming language.
  • Standard rules apply for your answer with default I/O rules, so you are allowed to use STDIN/STDOUT, functions/method with the proper parameters and return-type, full programs. Your call.
  • Default Loopholes are forbidden.
  • If possible, please add a link with a test for your code (i.e. TIO).
  • Also, adding an explanation for your answer is highly recommended.

Test cases:

Input:  "this is a clock cipher"
Output: "19:7:8:18:00:8:18:00:AM:00:2:11:14:2:10:00:2:8:15:7:4:17"

Input:  "test"
Output: "19:4:18:19"

Input:  "what time is it"
Output: "22:7:AM:19:00:19:8:12:4:00:8:18:00:8:19"

Input:  "acegikmoqsuwy bdfhjlnprtvxz"
Output: "AM:2:4:6:8:10:12:14:16:18:20:22:24:00:1:3:5:7:9:11:13:15:17:19:21:23:PM"

Input:  "easy peazy"
Output: "4:AM:18:24:00:15:4:AM:PM:24"
  • \$\begingroup\$ Related \$\endgroup\$ – Kevin Cruijssen Jan 4 '19 at 7:40
  • \$\begingroup\$ Is it allowed to output [7, ":", 8, ":", "00", ":", 1, ":", 14, ":", 1] for hi bob, or must one join the result? By the way, neat cipher! \$\endgroup\$ – Mr. Xcoder Jan 4 '19 at 9:27
  • \$\begingroup\$ @Mr.Xcoder Sorry, for the sake of the cipher theme I'd say it should be joined to a single string (or the entire thing as a list of characters like ['7', ':', '8', ':', '0', '0', ':', '1', ':', '1', '4', ':', '1']). \$\endgroup\$ – Kevin Cruijssen Jan 4 '19 at 9:32

14 Answers 14


Python 2, 74 72 bytes

lambda s:':'.join(['AM','PM','00',`ord(c)-97`]['az '.find(c)]for c in s)

Try it online!

Takes input as all lowercase


05AB1E, 22 21 bytes


Try it online! or as a Test Suite

Some alternate 21 byte solutions:

  • \$\begingroup\$ Nice answer, I managed to get 23 bytes through multiple approaches (one of which was my currently deleted answer). That's a neat way to arrange your stack to save a byte! \$\endgroup\$ – Mr. Xcoder Jan 4 '19 at 9:41
  • 1
    \$\begingroup\$ An alternate 22 byter combining our answers: Try it Online! \$\endgroup\$ – Mr. Xcoder Jan 4 '19 at 9:43
  • \$\begingroup\$ @Mr.Xcoder: My first idea actually looked like that, but 2 bytes worse because I didn't remember that ª had changed :) \$\endgroup\$ – Emigna Jan 4 '19 at 9:48
  • \$\begingroup\$ I've found a 20 byter using a portion of @Mr.Xcoder's approach, but I'll let you figure it out yourself before I reveil it. :) \$\endgroup\$ – Kevin Cruijssen Jan 4 '19 at 10:57
  • 1
    \$\begingroup\$ @KevinCruijssen: I'll let you know after I've looked some more ;) \$\endgroup\$ – Emigna Jan 4 '19 at 13:39

Perl 6, 47 bytes

*.ords>>.&{<<00 AM{1..24}PM>>[$_%32]}.join(":")

Try it online!

Anonymous Whatever lambda that takes a string of either case and returns the encrypted string.


*.ords>>.&{                         } # Map the ordinal values to
           <<              >>[$_%32]  # The index in the list
              00 AM{1..24}PM  # 00, AM, the numbers 1 to 24 and PM
                                     .join(":")   # And join with colons

Pyth, 25 bytes


Try it online here, or verify all the test cases at once here.

j\:m@+++"AM"S24"PM""00"xGdQ   Implicit: Q=eval(input()), G=lowercase alphabet
                              Trailing dQ inferred
            S24               [1-24]
       +"AM"                  Prepend "AM"
      +        "PM"           Append "PM"
     +             "00"       Append "00" - this is the dictionary
   m                      Q   Map each element of Q, as d, using:
                       xGd      Get the index of d in G, -1 if not present (i.e. space)
    @                           Get the element from the dictionary at the above index
j\:                           Join the result on ":", implicit print

JavaScript (Node.js), 72 bytes

Takes input in lowercase.


Try it online!


Java (JDK), 95 bytes

s->{int a=0;for(var c:s)System.out.print((a++<1?"":":")+(c<33?"00":c<66?"AM":c>89?"PM":c-65));}

Try it online!


  • -1 byte thanks to Kevin Cruijssen
  • \$\begingroup\$ One easy golf: char to var. :) \$\endgroup\$ – Kevin Cruijssen Jan 4 '19 at 11:00
  • \$\begingroup\$ Thanks! So obvious now that you show it to me... \$\endgroup\$ – Olivier Grégoire Jan 4 '19 at 11:02

C# (Visual C# Interactive Compiler), 70 bytes


Takes input as a string of lowercase letters. First checks if the char is a space, and if it is, converts it to 00. Next, it checks for if the char is an A, and converts it to AM. It checks again for Z and converts it to PM if it is. Lastly, if the char passes all the checks, it gets converted to its alphabetic order-1.

-2 bytes thanks to @dana

Try it online!

// Input taking a string
s => 
// Join the following IEnumerable<char> with a ":" character
// Map all the characters in the string
s.Select(a => 
// Is the char less than 33, aka a space?
a < 33 ? 
// If so, it's a "00"
// Else, is this an 'A'?
: a < 66 ?
// If so, convert it to "AM"
"AM" : 
// If it's not 'A' or a space, could it be a 'Z'?
a > 89 ?
// If it is, turn the character into "PM"
"PM" : 
// If it fails all of the checks above, get the characters position in the alphabet and subtract one from that.
a % 65 + ""))

Ruby, 49 bytes


Try it online!

Port of Jo King's Perl answer. Takes input as an array of chars, returns a string with AM/PM in uppercase.


Red, 124 121 110 109 bytes

func[s][replace/all form collect[forall s[keep switch/default
c: -97 + s/1[0['AM]25['PM]-65["00"]][c]]]sp":"]

Try it online!


05AB1E, 20 bytes


Greatly inspired by @Mr.Xcoder's 22-byter in the comment of the existing 05AB1E answer by @Emigna.

Takes the input as a list of lowercase characters (would be 21 bytes with a leading S if I take the input as a string).

Try it online or verify all test cases.


':ý            '# Join the (implicit) input list of characters by ":"
                #  i.e. ["e","a","s","y"," ","p","e","a","z","y"] → "e:a:s:y: :p:e:a:z:y"
ð00:            # Replace all spaces " " with "00"
                #  i.e. "e:a:s:y: :p:e:a:z:y" → "e:a:s:y:00:p:e:a:z:y"
A               # Push the lowercase alphabet
 24L            # Push a list in the range [1,24]
    „AMš        # Prepend "AM" at the start of this list
        „PMª    # And append "PM" at the end of the list
            ‡   # Transliterate; mapping letters to the list-items at the same indices
                # (and output the result implicitly)
                #  i.e. "e:a:s:y:00:p:e:a:z:y" → "4:AM:18:24:00:15:4:AM:PM:24"
  • 1
    \$\begingroup\$ Ah yes. Replacing the space separately saves a byte. I should have tried that. Nice :) \$\endgroup\$ – Emigna Jan 4 '19 at 14:41

Tcl, 100 bytes

proc C s {join [lmap c [split $s ""] {scan $c %c v
expr $v==65?"AM":$v==90?"PM":$v==32?00:$v-65}] :}

Try it online!


C# (Visual C# Interactive Compiler), 98 bytes

s=>string.Join(':',s.Select(c=>"az ".Contains(c)?new[]{"AM","PM","00"}["az ".IndexOf(c)]:c-97+""))

Takes input as a (lowercase) char array. Try it online!

  • \$\begingroup\$ 82 bytes: s=>string.Join(':',s.Select(c=>new[]{c-97+"","AM","PM","00"}["az ".IndexOf(c)+1])). \$\endgroup\$ – dana Jan 5 '19 at 12:45

Charcoal, 26 bytes

UB:Fθ«→≡ι ×0²a¦AM¦z¦PMI⌕βι

Try it online! Link is to verbose version of code. Takes input in lower case (can trivially be changed to upper case). Explanation:


Set the background character to :. This fills in the gaps between the output values created by the right movement.


Loop over each character, leaving a gap each time. (The first move has no effect as the canvas is still empty at this point.)

≡ι ×0²a¦AM¦z¦PM

Switch on the character and if it's space, a or z then output the appropriate code. I use ×0² instead of 00 here as the latter would cost two bytes in additional separators.


Otherwise output the letter's 0-indexed position in the lower case alphabet as a string.


Jelly, 24 bytes


Try it online!


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