69 lines
3.1 KiB
Erlang
69 lines
3.1 KiB
Erlang
-module(day16).
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-export([start/0]).
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dance([], Registers)
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-> Registers;
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dance([Head|Tail], Registers)
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-> Instr = string:slice(Head, 0, 1),
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Args = string:slice(Head, 1),
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NewRegisters = process_instruction(Instr, Args, Registers),
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dance(Tail, NewRegisters).
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process_instruction(Instr, Args, Registers)
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when Instr == <<"s">> -> Len = string:length(Registers),
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{ Count, _ } = string:to_integer(Args),
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Index = Len - Count,
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First = string:slice(Registers, Index),
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Second = string:slice(Registers, 0, Index),
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string:concat(First, Second);
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process_instruction(Instr, Args, Registers)
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when Instr == <<"x">> -> [FirstRegister|Rest] = re:split(Args, "/"),
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[SecondRegister|_] = Rest,
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{ FirstIndex, _ } = string:to_integer(FirstRegister),
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{ SecondIndex, _ } = string:to_integer(SecondRegister),
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swap_registers(FirstIndex, SecondIndex, Registers);
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process_instruction(Instr, Args, Registers)
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when Instr == <<"p">> -> [FirstRegister|Rest] = re:split(Args, "/"),
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[SecondRegister|_] = Rest,
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IndexA = char_index(FirstRegister, Registers),
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IndexB = char_index(SecondRegister, Registers),
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swap_registers(IndexA, IndexB, Registers).
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char_index(Char, String)
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-> StrLen = string:length(String),
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StrLen - string:length(string:find(String, Char)).
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find_char_index(Index)
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when Index == nomatch -> 0;
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find_char_index(Index)
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-> Index.
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swap_registers(A, B, Registers)
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when B < A -> swap_registers(B, A, Registers);
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swap_registers(A, B, Registers)
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-> RegisterList = list_to_tuple(Registers),
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ValueA = element(A + 1, RegisterList),
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ValueB = element(B + 1, RegisterList),
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tuple_to_list(setelement(B + 1, setelement(A + 1, RegisterList, ValueB), ValueA)).
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dance_countdown(Steps, Instructions, Registers)
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-> dance_countdown(Steps, Instructions, Registers, Steps, []).
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dance_countdown(Steps, _Instructions, Registers, _OriginalSteps, _PreviousSteps)
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when Steps == 0 -> Registers;
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dance_countdown(Steps, Instructions, Registers, OriginalSteps, PreviousSteps)
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-> CurrentRegisters = dance(Instructions, Registers),
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Found = lists:any(fun(X) -> string:equal(X, CurrentRegisters) end, PreviousSteps),
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if Found -> Index = OriginalSteps rem length(PreviousSteps),
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lists:nth(Index, PreviousSteps);
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true -> dance_countdown(Steps - 1, Instructions, CurrentRegisters, OriginalSteps, lists:append(PreviousSteps, [CurrentRegisters]))
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end.
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start()
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-> SampleInstructions = re:split("s1,x3/4,pe/b", ","),
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io:fwrite("~p~n", [dance(SampleInstructions, "abcde")]),
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{ ok, File } = file:read_file("input"),
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InputInstructions = re:split(unicode:characters_to_list(string:chomp(File)), ","),
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io:fwrite("~p~n", [dance(InputInstructions, "abcdefghijklmnop")]),
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io:fwrite("~p~n", [dance_countdown(1000000000, InputInstructions, "abcdefghijklmnop")]).
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