Power set: Difference between revisions

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 ===Single-Functor Definition===
-<lang Prolog>power_set(T, PS) :-
+<lang Prolog>power_set( [], [[]]).
-	bagof(PS1, power_set(T, [], PS1), PS).
+power_set( [X|Xs], PS) :-
+  power_set(Xs, PS1),
+  maplist( append([X]), PS1, PS2 ), % i.e. prepend X to each PS1
-power_set(T, PS, PS1) :-
+  append(PS1, PS2, PS).</lang>
-	select(E, T, T1), !,
-	append(PS, [E], PST),
-	( PST = PS1;  power_set(T1, PS, PS1);  power_set(T1, PST, PS1)).
-power_set([], [], []).
-</lang>
 Output :
+<pre>
-<pre> ?- power_set([1,2,3,4], L).
+:- power_set([1,2,3,4,5,6,7,8], X), length(X,N), writeln(N).
-L = [[1],[2],[3],[4],[],[3,4],[2,3],[2,4],[2,3,4],[1,2],[1,3],[1,4],[1,3,4],[1,2,3],[1,2,4],[1,2,3,4]].
 </pre>