62 lines
1.2 KiB
Prolog
62 lines
1.2 KiB
Prolog
dutch_flag(N) :-
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length(L, N),
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% create the list to sort
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repeat,
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maplist(init,L),
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\+is_dutch_flag(L) ,
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writeln(L),
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test_sorted(L),
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foldl(\X^Y^Z^(Y = [Red, White, Blue],
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( X = blue
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-> append_dl(Blue, [X|U]-U, Blue1),
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Z = [Red, White, Blue1]
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; X = red
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-> append_dl(Red, [X|U]-U, Red1),
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Z = [Red1, White, Blue]
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; append_dl(White, [X|U]-U, White1),
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Z = [Red, White1, Blue])),
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L, [R-R, W-W, B-B], [R1, W1, B1]),
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append_dl(R1, W1, B1, Flag-[]),
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write(Flag), nl,
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test_sorted(Flag).
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% append lists in O(1)
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append_dl(A-B, B-C, A-C).
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append_dl(A-B, B-C, C-D, A-D).
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init(C) :-
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R is random(3),
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nth0(R, [blue, red, white], C).
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test_sorted(Flag) :-
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( is_dutch_flag(Flag)
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-> write('it is a dutch flag')
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; write('it is not a dutch flag')),
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nl,nl.
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% First color must be red
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is_dutch_flag([red | T]) :-
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is_dutch_flag_red(T).
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is_dutch_flag_red([red|T]) :-
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is_dutch_flag_red(T);
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% second color must be white
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T = [white | T1],
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is_dutch_flag_white(T1).
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is_dutch_flag_white([white | T]) :-
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is_dutch_flag_white(T);
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% last one must be blue
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T = [blue | T1],
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is_dutch_flag_blue(T1).
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is_dutch_flag_blue([blue | T]) :-
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is_dutch_flag_blue(T).
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is_dutch_flag_blue([]).
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