[plt-scheme] Permutation correct way to do it ?

But you're using an accumulator, violating the design recipe of the  
section in which the problem lives. 60%

-- Matthias




On Apr 30, 2008, at 5:22 AM, Rocky wrote:

>
> Matthias said:
>>                                     This exercise is within reach
>> for someone who has never programmed before and follows the recipe;
>> if you fall in this group, systematically use the recipe and you will
>> get there. It is a stumbling block for people who have programmed
>> before and believe that I made up the design recipe to torture them.
>
> It's so simple, so very simple, that only a child can do it!
>
> Look Ma, no append ...
> --rocky
>
>
> (define (arrange aword)
>   (cond
>     ((empty? aword) (cons empty empty))
>     (else (inter/all (first aword) (arrange (rest aword))))))
>
>
> (define (inter/all elem alist)
>   (cond
>     ((empty? alist) empty)
>     (else
>      (inter/one empty
>                 elem
>                 (first alist)
>                 (inter/all elem (rest alist))))))
>
>
> (define (inter/one worms elem can alist)
>   (cond
>     ((empty? can) (cons (stuff worms (cons elem empty)) alist))
>     (else
>      (cons (stuff worms (cons elem can))
>            (inter/one (cons (first can) worms)
>                       elem
>                       (rest can)
>                       alist)))))
>
>
> (define (stuff worms can)
>   (cond
>     ((empty? worms) can)
>     (else (stuff (rest worms) (cons (first worms) can)))))
>
>
>
>        
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