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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
mjguru: 2015-11-28 10:17:49

No need for an array. This problem can be solved even without memoization (full on memoization).

Priyank: 2015-11-15 06:19:12

Just remember few imp. cases like 10, 20.

python_user: 2015-10-27 13:41:06

If you believe that your code is correct but is not passing some test cases, then look for ALL of the test cases mentioned in the comment section (till the last!!).

Last edit: 2015-10-27 13:41:21
Heartbreak_Kid: 2015-10-18 16:00:44

what will be the answer for "1101"?

Alex Anderson: 2015-10-11 00:35:50

Try for a more advanced version of this problem.

Dushyant Singh: 2015-10-07 18:51:34

@ senshiya: Because only 1,10 is only valid and 11,0 is not.

senshiya: 2015-10-07 18:01:51

how 110 gives 1

anandrohit: 2015-10-05 00:46:38

Awesome Question .. Not able to implement
but Finally Done :)
like a Fibonacci but take care if the Pairs are Forming or Not like 40 , 04

nonushikhar: 2015-10-01 01:56:06

easy ....just take care of 0 s in b/w the no. :)
check for 110 ans->1

carofe82: 2015-09-19 03:34:03

My first DP problem I solved. It put me to think. Thanks for the test cases!

Last edit: 2015-09-19 03:34:34

Added by:Adrian Kuegel
Time limit:0.341s
Source limit:50000B
Memory limit:1536MB
Cluster: Cube (Intel Pentium G860 3GHz)
Resource:ACM East Central North America Regional Programming Contest 2004