Closed. This question needs to be more focused. It is not currently accepting answers.
Want to improve this question? Update the question so it focuses on one problem only by editing this post.
Closed 3 years ago.
Improve this question
I was practicing the dynamic programming problem on SPOJ. But I have no idea how to solve this one.
Can anyone please help ME in solving http://www.spoj.pl/problems/ACODE/ problem on SPOJ
Thanks!
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
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.
Output
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.
Example
Input:
25114 1111111111 3333333333 0
Output:
6 89 1
Starting from the left, do the following:
Find how many words the sequence can be interpreted as (call that say x[k]) up to this point using a finite number of the values for previous calculated for points along the sequence.
Move to the next point.
If you still can't get it, you can take a look at the Welcome to Code Jam problem. It somewhat similar and has readily available explanations for it.
If you have a string of numbers as S, then, there are two cases possible :
1) only the first digit corresponds to an alphabet
2) the first two digits correspond to an alphabet. BUT, only if the first two digits don't form a number greater than 26.
Let S be of size n. Let f(Si) be the number of strings formed by last i digits. Note that you have to find f(Sn).
Using the above two rules, you can write a relation as :
If first two digits form a number <= 26 :
f ( Sk ) = f (Sk-1) + f (Sk-2)
If first two digits form a number > 26 :
Related
This question already has answers here:
Regular expression to match A, AB, ABC, but not AC. ("starts with")
(4 answers)
Closed 4 years ago.
I have an enumeration that I use as fixed parameter values to a program and I use regex to sanitize the user input.
I want the user to be able to enter a partial match to one of the values and accept that value and not other values.
For example if the enumeration is:
end
end now
start
swarm
condition
and the user entered
s
st
sta
etc...
it will be ok because it is part of start;
but if the user entered
ending
it will not be ok because its not part of any of the other words.
I know I can specify each permutation in a group (s|st|sta|star|start) and it will do the work, but doing this for around 12 different values seems very hard to maintain and "ugly'...
Is there an easier way to match a fixed values or sub of those fixed values?
I'm not searching for something that is specific to one engine/language (for example java code..)
Regex is not the correct tool for this job.
Just find the length of the user's input (call it N), then loop through your valid values and see if the first N characters of that value matches the input.
If only one item matches, you've got yourself a result! If more than one matches, you'll need more letters from the user to identify the correct one. And if none match, it's invalid.
Ok what I'm trying to do is to check for the presence of
"TestItem-1"
a number greater then 1
one of the possible words in the list of "KG. Kg, kg, Kilo(s) or Kilogram(s)"
Where any of the items could be in any order and within a 6 word limit of each other.
Has to be done in regex as there is no access to the underlying scripting engine
This is what I've got as there a way of checking greater then I decided to use a range of 1-999 for the number check.
\b(?:[T|t]estItem-1\W+(?:\w+\W+){1,6}(^[0-9]|[1-9][0-9]|[1-9][0-9][0-9])$)\W+(?:\w+\W+){1,6}[K|k]il[o|os]|[K|k][[G|GS]|[g|gs]]|[|K|k]ilogra[m|ms]\b
Examples of what I need to find would be like -
"TestItem-1 is unstable in quanties above 12 Kilograms"
"1 Kilogram of TestItem-1"
While I wouldn't want to find -
"15 units of TestItem-1"
I know that what I got isn't working each section appears to work independently of each other but not together.
I pass this over to far greater minds then mine :)
You can try something like this:
\b(?:[2-9]|\d\d+)\b\s\b(?:KG.|Kg,|kg,|Kilos?|Kilograms?)\b(?:\S+\s){0,6}\bTestItem-1\b|\bTestItem-1\b(?:\S+\s){0,6}\b(?:[2-9]|\d\d+)\b\s\b(?:KG.|Kg,|kg,|Kilos?|Kilograms?)\b
Not ideal with the duplication but without lookarounds that's the best I could think of. I'll try and improve it in a bit.
I would like to know how can I construct a regex to know if a number in base 2 (binary) is multiple of 3. I had read in this thread Check if a number is divisible by 3 but they dont do it with a regex, and the graph someone drew is wrong(because it doesn't accept even numbers). I have tried with: ((1+)(0*)(1+))(0) but it doesn't works for some values. Hope you can help me.
UPDATE:
Ok, thanks all for your help, now I know how to draw the NFA, here I left the graph and the regular expresion:
In the graph, the states are the number in base 10 mod 3.
For example: to go to state 1 you have to have 1, then you can add 1 or 0, if you add 1, you would have 11(3 in base 10), and this number mod 3 is 0 then you draw the arc to the state 0.
((0*)((11)*)((1((00) *)1) *)(101 *(0|((00) *1 *) *0)1) *(1(000)+1*01)*) *
And the other regex works, but this is shorter.
Thanks a lot :)
I know this is an old question, but an efficient answer is yet to be given and this question pops up first for "binary divisible by 3 regex" on Google.
Based on the DFA proposed by the author, a ridiculously short regex can be generated by simplifying the routes a binary string can take through the DFA.
The simplest one, using only state A, is:
0*
Including state B:
0*(11)*0*
Including state C:
0*(1(01*0)*1)*0*
And include the fact that after going back to state A, the whole process can be started again.
0*((1(01*0)*1)*0*)*
Using some basic regex rules, this simplifies to
(1(01*0)*1|0)*
Have a nice day.
If I may plug my solution for this code golf question! It's a piece of JavaScript that generates regexes (probably inefficiently, but does the job) for divisibility for each base.
This is what it generates for divisibility by 3 in base 2:
/^((((0+)?1)(10*1)*0)(0(10*1)*0|1)*(0(10*1)*(1(0+)?))|(((0+)?1)(10*1)*(1(0+)?)|(0(0+)?)))$/
Edit: comparing to Asmor's, probably very inefficient :)
Edit 2: Also, this is a duplicate of this question.
For some who is learning and searching how to do this:
see this video:
https://www.youtube.com/watch?v=SmT1DXLl3f4&t=138s
write state quations and solve them with Axden's Theorem
The way I did is visible in the image-result is the same as pointed out by user #Kert Ojasoo. I hope i did it corretly because i spent 2 days to solve it...
n+2n = 3n. Thus, 2 adjacent bits set to 1 denote a multiple of 3. If there are an odd number of adjacent 1s, that would not be 3.
So I'd propose this regex:
(0*(11)?)+
I have a list of numbers that I want to find at least 3 of...
here is an example
I have a large list of numbers in a sql database in the format of (for example)
01-02-03-04-05-06
06-08-19-24-25-36
etc etc
basically 6 random numbers between 0 and 99.
Now I want to find the strings where at least 3 of a set of given numbers occurs.
For example:
given: 01-02-03-10-11-12
return the strings that have at least 3 of those numbers in them.
eg
01-05-06-09-10-12 would match
03-08-10-12-18-22 would match
03-09-12-18-22-38 would not
I am thinking that there might be some algorithm or even regular expression that could match this... but my lack of computer science textbook experience is tripping me up I think.
No - this is not a homework question! This is for an actual application!
I am developing in ruby, but any language answer would be appreciated
You can use a string replacement to replace - with | to turn 01-02-03-10-11-12 into 01|02|03|10|11|12. Then wrap it like this:
((01|02|03|10|11|12).*){3}
This will find any of the digit pairs, then ignore any number of characters... 3 times. If it matches, then success.
Closed. This question is opinion-based. It is not currently accepting answers.
Want to improve this question? Update the question so it can be answered with facts and citations by editing this post.
Closed 9 years ago.
Improve this question
I'm thinking of presenting questions in the form of "here is your input: [foo], here are the capture groups/results: [bar]" (and maybe writing a small script to test their answers for my results).
What are some good regex questions to ask? I need everything from beginner questions like "validate a 4 digit number" to "extract postal codes from addresses".
A few that I can think off the top of my head:
Phone numbers in any format e.g. 555-5555, 555 55 55 55, (555) 555-555 etc.
Remove all html tags from text.
Match social security number (Finnish one is easy;)
All IP addresses
IP addresses with shorthand netmask (xx.xx.xx.xx/yy)
There's a bunch of examples of various regular expression techniques over at www.regular-expressions.info - everything for simple literal matching to backreferences and lookahead.
To keep things a bit more interesting than the usual email/phone/url stuff, try looking for more original exercises. Avoid boredom.
For example, have a look at the Forsysth-Edwards Notation which is used for describing a particular board position of a chess game.
Have your students validate and extract all the bits of information from a string like this:
rnbqkbnr/pp1ppppp/8/2p5/4P3/5N2/PPPP1PPP/RNBQKB1R b KQkq - 1 2
Additionaly, have a look at algebraic chess notation, used to describe moves. Extract chess moves out of a piece of text (and make them bold).
1. e4 e5 2. Nf3 Black now defends his pawn 2...Nc6 3. Bb5 Black threatens c4
Validate phone numbers (extract area code + rest of number with grouping) (Assuming US phone number, otherwise generalize for you style)
Play around with validating email address (probably want to tell the students that this is hugely complicated regular expression but for simple ones it is pretty straight forward)
regexplib.com has a good library you can search through for examples.
H0w about extract first name, middle name, last name, personal suffix (Jr., III, etc.) from a format like:
Smith III, John Paul
How about Reg Ex to remove line breaks and tabs from the input
I would start with the common ones:
validate email
validate phone number
separate the parts of a URL
Be cruel. Tell them parse HTML.
RegEx match open tags except XHTML self-contained tags
Are you teaching them theory of finite automata as well?
Here is a good one: parse the addresses of churches correctly from this badly structured format (copy and paste it as text first)
http://www.churchangel.com/WEBNY/newhart.htm
I'm a fan of parsing date strings. Define a few common data formats, as well as time and date-time formats. These are often good exercises because some dates are simple mixes of digits and punctuation. There's a limited degree of freedom in parsing dates.
Just to throw them for a loop, why not reword a question or two to suggest that they write a regular expression to generate data fitting a specific pattern like email addresses, phone numbers, etc.? It's the same thing as validating, but can help them get out of the mindset that regex is just for validation (whereas the data generation tool in visual studio uses regex to randomly generate data).
Rather than teaching examples based from the data set, I would do examples from the perspective of the rule set to get basics across. Give them simple examples to solve that leads them to use ONE of several basic groupings in each solution. Then have a couple of "compound" regex's at the end.
Simple:
s/abc/def/
Spinners and special characters:
s/a\s*b/abc/
Grouping:
s/[abc]/def/
Backreference:
s/ab(c)/def$1/
Anchors:
s/^fred/wilma/
s/$rubble/and betty/
Modifiers:
s/Abcd/def/gi
After this, I would give a few examples illustrating the pitfalls of trying to match html tags or other strings that shouldn't be done with regex's to show the limitations.
Try to think of some tests that don't include ones that can be found with Google.
Asking a email validator should pose no trouble finding..
Try something like a 5 proof test.
Input 5 digit. Sum up each digit must be dividable by five: 12345 = 1+2+3+4+5 = 15 / 5 = 3(.0)