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53 lines
1.3 KiB
Erlang
53 lines
1.3 KiB
Erlang
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% Find the sum of all the even-valued terms in the Fibonacci sequence which do not exceed four million.
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% Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:
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% 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...
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% Find the sum of all the even-valued terms in the sequence which do not exceed four million.
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-module(e002).
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-export([
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main/1,
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fibonacci_max/1
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]).
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fibonacci_max(Max) ->
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fibonacci_max_([], Max).
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fibonacci_max_([], Max) ->
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if
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Max < 1 ->
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[];
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true ->
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fibonacci_max_([1], Max)
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end;
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fibonacci_max_([N], Max) ->
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Next = N + N,
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if
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Max < Next ->
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[N];
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true ->
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fibonacci_max_([Next, N], Max)
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end;
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fibonacci_max_([N1, N2 | Seq], Max) ->
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Next = N1 + N2,
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if
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Max < Next ->
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[N1, N2 | Seq];
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true ->
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fibonacci_max_([Next, N1, N2 | Seq], Max)
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end.
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sum_if_even([]) ->
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0;
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sum_if_even([N | Seq]) ->
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if
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N rem 2 == 0 ->
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N + sum_if_even(Seq);
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true ->
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sum_if_even(Seq)
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end.
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main(_) ->
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Max = 4000000,
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io:format("Sum for fibonacci <= ~w: ~w~n", [Max, sum_if_even(fibonacci_max(Max))]).
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