Data commit

Task/Van-Eck-sequence/Prolog/van-eck-sequence.pro

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+van_eck_init(v(0, 0, _assoc)):-
+    empty_assoc(_assoc).
+
+van_eck_next(v(Index, Last_term, Last_pos), v(Index1, Next_term, Last_pos1)):-
+    (get_assoc(Last_term, Last_pos, V) ->
+        Next_term is Index - V
+        ;
+        Next_term = 0
+    ),
+    Index1 is Index + 1,
+    put_assoc(Last_term, Last_pos, Index, Last_pos1).
+
+van_eck_sequence(N, Seq):-
+    van_eck_init(V),
+    van_eck_sequence(N, V, Seq).
+
+van_eck_sequence(0, _, []):-!.
+van_eck_sequence(N, V, [Term|Rest]):-
+    V = v(_, Term, _),
+    van_eck_next(V, V1),
+    N1 is N - 1,
+    van_eck_sequence(N1, V1, Rest).
+
+write_list(From, To, _, _):-
+    To < From,
+    !.
+write_list(_, _, _, []):-!.
+write_list(From, To, N, [_|Rest]):-
+    From > N,
+    !,
+    N1 is N + 1,
+    write_list(From, To, N1, Rest).
+write_list(From, To, N, [E|Rest]):-
+    writef('%t ', [E]),
+    F1 is From + 1,
+    N1 is N + 1,
+    write_list(F1, To, N1, Rest).
+
+write_list(From, To, List):-
+    write_list(From, To, 1, List),
+    nl.
+
+main:-
+    van_eck_sequence(1000, Seq),
+    writeln('First 10 terms of the Van Eck sequence:'),
+    write_list(1, 10, Seq),
+    writeln('Terms 991 to 1000 of the Van Eck sequence:'),
+    write_list(991, 1000, Seq).