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From: schang@uiucdcs.UUCP
Newsgroups: net.micro.pc
Subject: Re: Programing Puzzle - (nf)
Message-ID: <24700048@uiucdcs.UUCP>
Date: Sat, 21-Jul-84 16:57:00 EDT
Article-I.D.: uiucdcs.24700048
Posted: Sat Jul 21 16:57:00 1984
Date-Received: Sun, 22-Jul-84 06:21:43 EDT
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Nf-ID: #R:inuxc:-99400:uiucdcs:24700048:000:990
Nf-From: uiucdcs!schang    Jul 21 15:57:00 1984

#R:inuxc:-99400:uiucdcs:24700048:000:990
uiucdcs!schang    Jul 21 15:57:00 1984


[]

Prolog is probably the best language to solve this problem, it took me
less than 15 minutes to write and test the following :

>     % 'permut' returns one permutation of 'List'. It consists of taking one
>     % element from 'List' and then taking one permutation of the remaining
>     % list.
>     
>     permut(List, [Elt | Tail]) :-
>     		pickup_one(Elt,List,Remaining),
>     		permut( Remaining, Tail).
>     permut( [], []).
>     
>     pickup_one( X, [X | T], T).
>     pickup_one( X, [Y | T], [Y | Z]) :-
>     		pickup_one( X, T, Z).

Here is the result of the program :

>
>     UNSW - PROLOG (IBM PC)
>     : permut([1,2,3], X)?
>   
>     X = [1, 2, 3]
>   
>     X = [1, 3, 2]
>   
>     X = [2, 1, 3]
>   
>     X = [2, 3, 1]
>   
>     X = [3, 1, 2]
>   
>     X = [3, 2, 1]
>     : ^D


			     Thierry Schang
			...!{ihnp4, pur-ee, parsec}!uiucdcs!schang

			Department of Computer Science
			University of Illinois
			1304, W. Springfield
			Urbana, Il 61801