From: Marc Tfardy <tfardol@very-tfardol.com>
To: help-gnu-emacs@gnu.org
Subject: Re: All Possible Combinations
Date: Wed, 03 Jun 2009 20:50:00 +0200 [thread overview]
Message-ID: <h06gkp$d55$1@news.onet.pl> (raw)
In-Reply-To: <778c22e3-3233-4cec-899e-c9f77208155a@z14g2000yqa.googlegroups.com>
Nordlöw schrieb:
> Hey!
>
> I want a function that generates all possible combinations (ordering)
> of the elements in a list (or sequence if possible). Here is my
> mockup:
>
> (defun all-combinations (n)
> "Generate a listing of all the possible combinations of the
> elements in the sequence N. Time-Complexity is N!"
> (let (all)
> all))
>
> For example (all-combinations '(a b c)) should return '((a b c) (a c
> b) (b a c) (b c a) (c a b) (c b a))
>
> Has somebody written such a function, preferrably in an iterative
> rather than recursive way.
Here you find working common lisp version:
http://www.perlmonks.org/?node_id=485066
(defun permutations (bag)
"Return a list of all the permutations of the input."
;; If the input is nil, there is only one permutation:
;; nil itself
(if (null bag)
'(())
;; Otherwise, take an element, e, out of the bag.
;; Generate all permutations of the remaining elements,
;; And add e to the front of each of these.
;; Do this for all possible e to generate all permutations.
(mapcan #'(lambda (e)
(mapcar #'(lambda (p) (cons e p))
(permutations
(remove e bag :count 1))))
bag)))
Now replace 'remove' with 'remove*' and this works in emacs lisp, too.
regards
Marc
next prev parent reply other threads:[~2009-06-03 18:50 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-06-03 9:09 All Possible Combinations Nordlöw
2009-06-03 9:53 ` Pascal J. Bourguignon
2009-06-03 13:36 ` B. T. Raven
2009-06-03 9:55 ` Lennart Borgman
2009-06-03 18:50 ` Marc Tfardy [this message]
2009-06-04 6:08 ` Nordlöw
2009-06-04 7:20 ` Marc Tfardy
2009-06-04 16:25 ` B. T. Raven
2009-06-05 15:49 ` Thierry Volpiatto
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