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MySQL regexp / regular expressions help - scrabble solver

Posted on 2009-04-13
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Last Modified: 2013-12-12
I'm trying to build a scrabble solver - I can make it work, but not the way I want it to - basically I get all words less than or equal to the length of the input string, then walk through the restultset in my php script checking against the letter array built from the input string.

I know this is a bad - and slow - way to do it, and I'm sure there is a way to do it just from the query, but I'm struggling with this.

The example below assumes the input string is ABCDE, so finds all words which are 5 characters or less and only use the letters ABCDE - but the two problems with this are it allows letters to be repeated (which needs to be dependent on the input string), and it can't handle wildcards.

SELECT WORD FROM WORDLIST WHERE CHARACTER_LENGTH(WORD) <= 5 AND WORD NOT REGEXP '[^ABCDE]'

It would be quick enough to get the resultset and then filter out any words that use letters more than once (except of course if the input string contained eg. more than one 'A' and this is allowed), but this doesn't solve the wildcard problem.

I've looked at the mysql reference and I'm sure there must be a way to do this, but I've tried what seems like every combination and I'm not getting anywhere.

Does anyone have any suggestions? Is this actually possible through mysql alone?
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Question by:rockers07
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7 Comments
 
LVL 17

Expert Comment

by:akshah123
ID: 24130599
You should try following ...

SELECT WORD 
FROM WORDLIST 
WHERE WORD REGEXP '^[ABCDE]{5}$'

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Author Comment

by:rockers07
ID: 24130627
Thanks, but that only selects 5 letter words, and doesn't solve the duplicate letters or wildcard problems...
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LVL 17

Expert Comment

by:akshah123
ID: 24130798
You will not be able to solve the duplication problem within the query.  That's just not possible unless you want to provide all possible combinations.  

IF you need to solve this problem multiple times, it might make more sense to have this data in memory instead.  

In any case, your only option is to take care of that in php.
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Author Comment

by:rockers07
ID: 24131201
Duplication problem solved:

SELECT WORD FROM WORDLIST
WHERE CHARACTER_LENGTH(WORD) <= 5
AND WORD NOT REGEXP '[^ABCDE]'
AND LENGTH(WORD) - LENGTH(REPLACE(WORD, 'A', '')) <= 1
AND LENGTH(WORD) - LENGTH(REPLACE(WORD, 'B', '')) <= 1
AND LENGTH(WORD) - LENGTH(REPLACE(WORD, 'C', '')) <= 1
AND LENGTH(WORD) - LENGTH(REPLACE(WORD, 'D', '')) <= 1
AND LENGTH(WORD) - LENGTH(REPLACE(WORD, 'E', '')) <= 1

And change to <= 2 if the letter can appear twice etc.

Not sure that this is the most efficient method though - easy enough to process the duplications in PHP using substr_count(), and this is feasible if the result has already been filtered to the right length and characters - but it still feels like this should be possible through regexp.

I'm also still left with the wildcard problem.....
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LVL 41

Expert Comment

by:HonorGod
ID: 24131846
Use a GADDAG data structure...

http://www.cs.ubc.ca/local/reading/proceedings/spe91-95/spe/vol24/issue2/spe880.pdf

Which is a way of storing the entire (US English) Scrabble dictionary in such a way as to:

- consume lots less space
- make is very quick to search
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