29 lines
987 B
Erlang
29 lines
987 B
Erlang
-module(collatz).
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-export([main/0,collatz/1,coll/1,max_atz_under/1]).
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collatz(1) -> 1;
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collatz(N) when N rem 2 == 0 -> 1 + collatz(N div 2);
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collatz(N) when N rem 2 > 0 -> 1 + collatz(3 * N +1).
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max_atz_under(N) ->
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F = fun (X) -> {collatz(X), X} end,
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{_, Index} = lists:max(lists:map(F, lists:seq(1, N))),
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Index.
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coll(1) -> [1];
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coll(N) when N rem 2 == 0 -> [N|coll(N div 2)];
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coll(N) -> [N|coll(3 * N + 1)].
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main() ->
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io:format("collatz(4) non-list total: ~w~n", [collatz(4)]),
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io:format("coll(4) with lists ~w~n", [coll(4)] ),
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Seq27 = coll(27),
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Seq1000 = coll(max_atz_under(100000)),
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io:format("coll(27) length: ~B~n", [length(Seq27)]),
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io:format("coll(27) first 4: ~w~n", [lists:sublist(Seq27, 4)]),
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io:format("collatz(27) last 4: ~w~n",
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[lists:nthtail(length(Seq27) - 4, Seq27)]),
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io:format("maximum N <= 100000..."),
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io:format("Max: ~w~n", [max_atz_under(100000)]),
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io:format("Total: ~w~n", [ length( Seq1000 ) ] ).
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