From: Robert Klemme <shortcutter@...>
Date: 2008-12-26T19:50:00+09:00
Subject: Re: Buiding anamgrams

On 26.12.2008 10:30, andrea wrote:
> I'm studying ruby (and I really love it even more than python) and I
> want to do a little exercise.

Welcome to the pack!  What a nice Christmas occupation. :-)

> I want to create an efficient module to generate every possible
> anagrams of a word, of any given size...

Do you really mean "anagrams" or rather "permutations"?  To decide on 
anagrams you likely need some kind of dictionary which is significantly 
more difficult than just permuting.

> I already done this in python, I want to see how can it be elegant in
> ruby...
> I need a good permutation algorithm (this
> http://www.cut-the-knot.org/Curriculum/Combinatorics/JohnsonTrotter.shtml
> works fine) and I'd like to use enumerators in the best and most
> efficient way.

 From 1.8.7 on you can do this

irb(main):009:0> "abc".scan(/./).permutation {|x| p x.join}
"abc"
"acb"
"bac"
"bca"
"cab"
"cba"
=> ["a", "b", "c"]
irb(main):010:0> "abc".chars.to_a.permutation {|x| p x.join}
"abc"
"acb"
"bac"
"bca"
"cab"
"cba"
=> ["a", "b", "c"]
irb(main):011:0>

Now you only need a filter that properly decides which of those is a 
proper word and use that to decide which words to print and which not.

> I also looked at callcc which is great for backtracking, could be used
> in this case??

I would try to avoid it as it makes code very hard to read - at least 
for me. :-)

> thanks for any help
> 
> A basic structure like that could be fine?
> class Anagrams
>   attr :word
>   include Enumerable
>   include Comparable
> 
>   def <=>(other)
>     self.word <=> other.word
>   end
> 
>   def each(&block)
>     @word.chars
>   end
> 
>   def initialize(word)
>     @word = word
>   end
> 
> end

What exactly should be the responsibility of this class?  Especially, 
why do you call it "anagrams" but store only one word in it?

Cheers

	robert

-- 
remember.guy do |as, often| as.you_can - without end