ACODE - Alphacode

Alice and Bob need to send secret messages to each other and are discussing ways to encode their messages:

Alice: “Let’s just use a very simple code: We’ll assign ‘A’ the code word 1, ‘B’ will be 2, and so on down to ‘Z’ being assigned 26.”

Bob: “That’s a stupid code, Alice. Suppose I send you the word ‘BEAN’ encoded as 25114. You could decode that in many different ways!”

Alice: “Sure you could, but what words would you get? Other than ‘BEAN’, you’d get ‘BEAAD’, ‘YAAD’, ‘YAN’, ‘YKD’ and ‘BEKD’. I think you would be able to figure out the correct decoding. And why would you send me the word ‘BEAN’ anyway?”

Bob: “OK, maybe that’s a bad example, but I bet you that if you got a string of length 5000 there would be tons of different decodings and with that many you would find at least two different ones that would make sense.”

Alice: “How many different decodings?”

Bob: “Jillions!”

For some reason, Alice is still unconvinced by Bob’s argument, so she requires a program that will determine how many decodings there can be for a given string using her code.


Input will consist of multiple input sets. Each set will consist of a single line of at most 5000 digits representing a valid encryption (for example, no line will begin with a 0). There will be no spaces between the digits. An input line of ‘0’ will terminate the input and should not be processed.


For each input set, output the number of possible decodings for the input string. All answers will be within the range of a 64 bit signed integer.






hide comments
sagnik_66: 2017-05-19 17:47:16

Nice problem!

slayerofcoding: 2017-05-19 06:59:17

I get the runtime error- SIGABRT. Any suggestion to overcome it....

horizon121: 2017-05-18 18:56:23

Did get a few WA's thanx to those Zeros otherwise its a nice dp problem..2nd one for me so it feels good:D
@narutomania 20022 is Invalid

narutoumania: 2017-05-17 07:26:18

20022 is it a valid input?
if it is how?

tikli_10: 2017-05-16 17:24:49

Why Alice, why?

giovanni_vm: 2017-05-10 20:10:32

The text should inform 01 to 09 and 010 to 026 is not a valid letter.

da_201501181: 2017-05-08 13:40:44

AC in one go..!! Excellent problem for beginners in DP..! Thanks to Logic_bomb for WA saving testcases.!!

If getting WA, try some of the following test cases.
226210 -> 3
301 -> 0
50 -> 0
1020 -> 1
2002-> 0
PS: Testcases by logic_bomb

helloitsme: 2017-05-04 14:32:22

My code in Python 3 passed all tests correctly mentioned in the comments , still it says wrong answer?
Whats the problem , Please help:(

hkuadithya: 2017-05-03 12:15:54

A true programmer will solve it without any recursion and DP array. You can do it more efficiently iteratively 0.00 AC (Fibonacci series using 3 variables).

As for detecting the invalid test cases such as "100" or "301", "111180" and so on, I used regex to find if such invalid pattern exists in the string. If it does, print "0" as the answer.

Thank you all for the test cases. They are a life saver.

Last edit: 2017-05-03 12:17:38
scube6897: 2017-05-01 18:03:05

Getting a WA despite passing all the tcs mentioned in the comments!Please help!

Last edit: 2017-05-01 18:04:16

Added by:Adrian Kuegel
Time limit:0.341s
Source limit:50000B
Memory limit:1536MB
Cluster: Cube (Intel G860)
Resource:ACM East Central North America Regional Programming Contest 2004