1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 | /* Magic sequence problem in B-Prolog. http://www.dcs.st-and.ac.uk/~ianm/CSPLib/prob/prob019/spec.html """ A magic sequence of length n is a sequence of integers x0 . . xn-1 between 0 and n-1, such that for all i in 0 to n-1, the number i occurs exactly xi times in the sequence. For instance, 6,2,1,0,0,0,1,0,0,0 is a magic sequence since 0 occurs 6 times in it, 1 occurs twice, ... """ Model created by Hakan Kjellerstrand, hakank@gmail.com*/% Licenced under CC-BY-4.0 : http://creativecommons.org/licenses/by/4.0/%% Reporting both time and backtracks%time2(Goal):- cputime(Start), statistics(backtracks, Backtracks1), call(Goal), statistics(backtracks, Backtracks2), cputime(End), T is (End-Start)/1000, Backtracks is Backtracks2 - Backtracks1, format('CPU time ~w seconds. Backtracks: ~d\n', [T, Backtracks]).go :- time2(solve(400,_Sequence)).go2 :- foreach(N in 4..40, [Sequence], time2(solve(N,Sequence)) ).solve(N, Sequence) :- format('\n~d: ',[N]), length(Sequence, N), Sequence :: 0..N-1, % Note: I would like to use global_cardinality/2 instead % but didn't get it right. foreach(I in 0..N-1, count(I,Sequence,#=,Sequence[I+1])), % Alternative % foreach(I in 0..N-1, exactly(Sequence[I+1],Sequence,I)), N #= sum(Sequence), Integers @= [ I : I in 0..N-1], scalar_product(Integers, Sequence, #=, N), % labeling([inout],Sequence) -> labeling([degree],Sequence) -> % labeling([ff],Sequence) -> writeln(Sequence) ; writeln('Something wrong happened.'), true. |