Data commit

Task/Hofstadter-Q-sequence/Erlang/hofstadter-q-sequence.erl

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+%% @author Jan Willem Luiten <jwl@secondmove.com>
+%% Hofstadter Q Sequence for Rosetta Code
+
+-module(hofstadter).
+-export([main/0]).
+-define(MAX, 100000).
+
+flip(V2, V1) when V1 > V2 -> 1;
+flip(_V2, _V1) -> 0.
+	
+list_terms(N, N, Acc) ->
+	io:format("~w~n", [array:get(N, Acc)]);
+list_terms(Max, N, Acc) ->
+	io:format("~w, ", [array:get(N, Acc)]),
+	list_terms(Max, N+1, Acc).
+
+hofstadter(N, N, Acc, Flips) ->
+	io:format("The first ten terms are: "),
+	list_terms(9, 0, Acc),
+	io:format("The 1000'th term is ~w~n", [array:get(999, Acc)]),
+	io:format("Number of flips: ~w~n", [Flips]);
+hofstadter(Max, N, Acc, Flips) ->
+	Qn1 = array:get(N-1, Acc),
+	Qn = array:get(N - Qn1, Acc) + array:get(N - array:get(N-2, Acc), Acc),
+	hofstadter(Max, N+1, array:set(N, Qn, Acc), Flips + flip(Qn, Qn1)).
+
+main() ->
+	Tmp = array:set(0, 1, array:new(?MAX)),
+	Acc = array:set(1, 1, Tmp),
+	hofstadter(?MAX, 2, Acc, 0).