N queens

Description

Naive generate-and-test program solving N queens

Source: The Art of Prolog

Download

Program source code: n_queens.pl

Listing

/*
 
   queens(N,Queens) :-
 
	Queens is a placement that solves the N queens problem,
 
	represented as a permutation of the list of numbers [1,2,...,N].
 
*/
 
 
 
     queens(N,Qs) :- range(1,N,Ns), permutation(Ns,Qs), safe(Qs).
 
 
 
/*
 
	safe(Qs) :- The placement Qs is safe.
 
*/     
 
     safe([Q|Qs]) :- safe(Qs), not attack(Q,Qs).
 
     safe([]).     
 
 
 
     attack(X,Xs) :- attack(X,1,Xs).
 
 
 
     attack(X,N,[Y|_]) :- X is Y+N ; X is Y-N.
 
     attack(X,N,[_|Ys]) :- N1 is N+1, attack(X,N1,Ys).
 
 
 
 
 
	permutation(Xs,[Z|Zs]) :- select(Z,Xs,Ys), permutation(Ys,Zs).
 
	permutation([],[]).
 
 
 
	select(X,[X|Xs],Xs).
 
	select(X,[Y|Ys],[Y|Zs]) :- select(X,Ys,Zs).
 
 
 
     range(M,N,[M|Ns]) :- M < N, M1 is M+1, range(M1,N,Ns).
 
     range(N,N,[N]).
 
 
 
%	Program 14.2: Naive generate-and-test pr
 
gram solving N queens

Comments

RTERR: 12:5 : Syntax error. Operator expected.

pl/prolog/pllib/n_queens.txt · ostatnio zmienione: 2017/07/17 08:08 (edycja zewnętrzna)
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