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+====== Dutch flag 2 ======
+{{tag>problem_solving}}
+===== Description =====
+Dutch Flag with difference-lists.
+**Source**:  The Art of Prolog
+===== Download =====
+Program source code: {{dutch_flag_2.pl}}
+===== Listing =====
+<code prolog>
+/*
+   dutch(Xs,RedsWhitesBlues) :-
+	RedsWhitesBlues is a list of elements of Xs ordered
+		by color: red, then white, then blue.
+*/
+	:- op(40,xfx,\).
+	dutch(Xs,RedsWhitesBlues) :-
+		distribute_dls(Xs,RedsWhitesBlues\WhitesBlues,
+			WhitesBlues\Blues,Blues\[]).
+/*
+    distribute_dls(Xs,Reds,Whites,Blues) :-
+	Reds,Whites,Blues are difference-lists of red, white,
+		and blue elements in Xs, respectively.
+*/
+	distribute_dls([red(X)|Xs],[red(X)|Reds]\Reds1,Whites,Blues) :-
+		distribute_dls(Xs,Reds\Reds1,Whites,Blues).
+	distribute_dls([white(X)|Xs],Reds,[white(X)|Whites]\Whites1,Blues) :-
+		distribute_dls(Xs,Reds,Whites\Whites1,Blues).
+	distribute_dls([blue(X)|Xs],Reds,Whites,[blue(X)|Blues]\Blues1) :-
+		distribute_dls(Xs,Reds,Whites,Blues\Blues1).
+	distribute_dls([],Reds\Reds,Whites\Whites,Blues\Blues).
+%	Program 15.6: Dutch Flag with difference-lists.
+</code>
+===== Comments =====

pl/prolog/pllib/dutch_flag_2.txt · ostatnio zmienione: 2019/06/27 15:50 (edycja zewnętrzna)

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