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pl:prolog:pllib:8_queens_3 [2019/06/27 15:50] (aktualna)
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 +====== 8 queens 3 ======
 +{{tag>​puzzle chess}}
 +===== Description =====
 +Program solves 8 queens problem
 +
 +**Source**: ​ PROLOG programming for artificial intelligence,​ 3rd Edition, Harlow, 2001, ISBN 0-201-40375-7.
 +===== Download =====
 +Program source code: {{prolog:​pllib:​8_queens_3.pl}}
 +===== Listing =====
 +<code prolog>
 +%  Figure 4.7  Program 1 for the eight queens problem.
 +
 +
 +% solution( BoardPosition) if
 +%   ​BoardPosition is a list of non-attacking queens
 +
 +solution( [] ).
 +
 +solution( [X/Y | Others] )  :-      % First queen at X/Y, other queens at Others
 +  solution( Others),
 +  member( Y, [1,​2,​3,​4,​5,​6,​7,​8] ),
 +  noattack( X/Y, Others). ​          % First queen does not attack others
 +
 +noattack( _, [] ).                  % Nothing to attack
 +
 +noattack( X/Y, [X1/Y1 | Others] )  :-
 +  Y =\= Y1,                         % Different Y-coordinates
 +  Y1-Y =\= X1-X,                    % Different diagonals
 +  Y1-Y =\= X-X1,
 +  noattack( X/Y, Others).
 +
 +member( Item, [Item | Rest] ).
 +
 +member( Item, [First | Rest] )  :-
 +  member( Item, Rest).
 +
 +% A solution template
 +
 +template( [1/​Y1,​2/​Y2,​3/​Y3,​4/​Y4,​5/​Y5,​6/​Y6,​7/​Y7,​8/​Y8] ).
 +</​code>​
 +===== Comments =====
  
pl/prolog/pllib/8_queens_3.txt · ostatnio zmienione: 2019/06/27 15:50 (edycja zewnętrzna)
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