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98fc3e45c0
Estimated hours taken: 0.02 tests/benchmarks/queens.m: Move the import of printlist into the implementation, where it belongs. This avoids a warning.
83 lines
1.3 KiB
Mathematica
83 lines
1.3 KiB
Mathematica
% 9-queens program
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:- module queens.
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:- interface.
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:- import_module list, int, io.
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:- pred main1(list(int)).
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:- mode main1(out) is nondet.
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:- pred main(io__state, io__state).
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:- mode main(di, uo) is cc_multi.
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:- implementation.
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:- import_module printlist.
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main1(Out) :-
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data(Data),
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queen(Data, Out).
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main -->
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( { data(Data), queen(Data, Out) } ->
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print_list(Out)
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;
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io__write_string("No solution\n")
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).
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:- pred data(list(int)).
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:- mode data(out) is det.
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:- pred queen(list(int), list(int)).
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:- mode queen(in, out) is nondet.
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:- pred qperm(list(int), list(int)).
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:- mode qperm(in, out) is nondet.
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:- pred qdelete(int, list(int), list(int)).
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:- mode qdelete(out, in, out) is nondet.
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:- pred safe(list(int)).
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:- mode safe(in) is semidet.
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:- pred nodiag(int, int, list(int)).
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:- mode nodiag(in, in, in) is semidet.
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data([1,2,3,4,5,6,7,8]).
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queen(Data, Out) :-
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qperm(Data, Out),
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safe(Out).
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qperm([], []).
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qperm([X|Y], K) :-
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qdelete(U, [X|Y], Z),
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K = [U|V],
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qperm(Z, V).
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qdelete(A, [A|L], L).
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qdelete(X, [A|Z], [A|R]) :-
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qdelete(X, Z, R).
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safe([]).
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safe([N|L]) :-
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nodiag(N, 1, L),
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safe(L).
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nodiag(_, _, []).
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nodiag(B, D, [N|L]) :-
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NmB is N - B,
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BmN is B - N,
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( D = NmB ->
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fail
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; D = BmN ->
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fail
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;
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true
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),
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D1 is D + 1,
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nodiag(B, D1, L).
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