Prolog "queens"

Admin User, erstellt 25. Okt. 2024
         /**
          * Prolog code for the 9x9-queens benchmark.
          *
          * Originally conceived in by Max Bezzel for the 8x8 checker board.
          * Used by Edsger Dijkstra to illustrate the
          * depth-first backtracking search algorithm.
          *
          * Warranty & Liability
          * To the extent permitted by applicable law and unless explicitly
          * otherwise agreed upon, XLOG Technologies AG makes no warranties
          * regarding the provided information. XLOG Technologies AG assumes
          * no liability that any problems might be solved with the information
          * provided by XLOG Technologies AG.
          *
          * Rights & License
          * All industrial property rights regarding the information - copyright
          * and patent rights in particular - are the sole property of XLOG
          * Technologies AG. If the company was not the originator of some
          * excerpts, XLOG Technologies AG has at least obtained the right to
          * reproduce, change and translate the information.
          *
          * Reproduction is restricted to the whole unaltered document. Reproduction
          * of the information is only allowed for non-commercial uses. Selling,
          * giving away or letting of the execution of the library is prohibited.
          * The library can be distributed as part of your applications and libraries
          * for execution provided this comment remains unchanged.
          *
          * Restrictions
          * Only to be distributed with programs that add significant and primary
          * functionality to the library. Not to be distributed with additional
          * software intended to replace any components of the library.
          *
          * Trademarks
          * Jekejeke is a registered trademark of XLOG Technologies AG.
          */
         
         % queens
         queens :-
            dataqueens(X),
            search(X, [], _).
         
         % dataqueens(-List)
         dataqueens([1,2,3,4,5,6,7,8,9]).
         
         /*****************************************************************/
         /* The Solver                                                    */
         /*****************************************************************/
         
         % nodiag(+List, +Integer, +Integer)
         nodiag([], _, _).
         nodiag([N|L], B, D) :-
             D =\= N - B,
             D =\= B - N,
             D1 is D + 1,
             nodiag(L, B, D1).
         
         % qdelete(+List, -Integer, +Integer, -List)
         qdelete(L, A, A, L).
         qdelete([H|T], X, A, [A|R]) :-
             qdelete(T, X, H, R).
         
         % search(+List, +List, -List)
         search([], _, []).
         search([H|T], History, [Q|M]) :-
             qdelete(T, Q, H, L1),
             nodiag(History, Q, 1),
             search(L1, [Q|History], M).
Prolog "queens"

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