40 lines
1.8 KiB
Erlang
40 lines
1.8 KiB
Erlang
-module(day6).
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-export([start/0]).
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index_of(Item, List) -> index_of(Item, List, 1).
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index_of(_, [], _) -> not_found;
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index_of(Item, [Item|_], Index) -> Index;
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index_of(Item, [_|Tl], Index) -> index_of(Item, Tl, Index+1).
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redistribute_banks(BankConfiguration)
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-> Max = lists:max(BankConfiguration),
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Index = index_of(Max, BankConfiguration) - 1,
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%io:fwrite("max ~B index ~B~n", [Max, Index]),
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RawArray = array:from_list(BankConfiguration),
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redistribute_banks(array:set(Index, 0, RawArray), Index, Max, length(BankConfiguration)).
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redistribute_banks(Array, _Index, RemainingBanks, _MaxSize)
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when RemainingBanks == 0 -> array:to_list(Array);
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redistribute_banks(Array, Index, RemainingBanks, MaxSize)
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-> Target = (Index + 1) rem MaxSize,
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OldBankValue = array:get(Target, Array),
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%io:fwrite("target ~B oldbankvalue ~B~n", [Target, OldBankValue]),
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redistribute_banks(array:set(Target, OldBankValue + 1, Array), Target, RemainingBanks - 1, MaxSize).
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steps_until_repeated(Input)
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-> steps_until_repeated(Input, [], []).
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steps_until_repeated(Input, Visited, UniqList)
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when length(Visited) > 0, length(UniqList) /= length(Visited) -> [_|PriorVisits] = Visited,
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InputIndex = index_of(Input, PriorVisits),
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VisitedLength = length(Visited),
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{VisitedLength,Input,InputIndex};
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steps_until_repeated(Input, Visited, _UniqList)
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-> NewConfiguration = redistribute_banks(Input),
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NewVisited = [NewConfiguration|Visited],
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steps_until_repeated(NewConfiguration, NewVisited, lists:usort(NewVisited)).
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start()
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-> io:fwrite("~p~n", [steps_until_repeated([0,2,7,0])]),
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io:fwrite("~p~n", [steps_until_repeated([4,1,15,12,0,9,9,5,5,8,7,3,14,5,12,3])]).
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