73 lines
2.7 KiB
Erlang
73 lines
2.7 KiB
Erlang
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-module(day19).
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-export([start/0]).
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find_start_col([Head|_Tail], Index)
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when Head == "|" -> Index;
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find_start_col([_Head|Tail], Index)
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-> find_start_col(Tail, Index + 1).
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map_input(InputList)
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-> map_input(InputList, dict:new(), 0).
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map_input([], Maze, _Row)
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-> Maze;
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map_input([Head|Tail], Maze, Row)
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-> NewMaze = map_row(re:split(string:chomp(Head), ""), Maze, 0, Row),
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map_input(Tail, NewMaze, Row + 1).
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map_row([], Maze, _Col, _Row)
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-> Maze;
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map_row([Head|Tail], Maze, Col, Row)
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-> map_row(Tail, dict:store({ Col, Row }, Head, Maze), Col + 1, Row).
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trace_maze(Maze, X, Y, Marked, VisitedChars, Steps, DeltaX, DeltaY)
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-> Key = { X, Y },
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Marked2 = dict:store(Key, 1, Marked),
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Value = dict:fetch(Key, Maze),
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if Value >= <<"A">>, Value =< <<"Z">> ->
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Terminal = is_terminal(Maze, X, Y, Marked2, DeltaX, DeltaY),
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if Terminal -> { VisitedChars, Steps };
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true -> trace_maze(Maze, X + DeltaX, Y + DeltaY, Marked2, lists:append(VisitedChars, [Value]), Steps + 1, DeltaX, DeltaY)
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end;
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Value == <<"+">> ->
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{ NewDeltaX, NewDeltaY } = find_new_direction(Maze, X, Y, Marked2),
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trace_maze(Maze, X + NewDeltaX, Y + NewDeltaY, Marked, VisitedChars, Steps + 1, NewDeltaX, NewDeltaY);
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true ->
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trace_maze(Maze, X + DeltaX, Y + DeltaY, Marked2, VisitedChars, Steps + 1, DeltaX, DeltaY)
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end.
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is_terminal(Maze, X, Y, Marked, DeltaX, DeltaY)
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-> NextVal = dict:fetch({ X + DeltaX, Y + DeltaY }, Maze),
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NextVal == <<" ">>.
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find_new_direction(Maze, X, Y, Marked)
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-> NorthVal = get_new_direction_val(Maze, X, Y - 1, Marked, <<"|">>),
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SouthVal = get_new_direction_val(Maze, X, Y + 1, Marked, <<"|">>),
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EastVal = get_new_direction_val(Maze, X + 1, Y, Marked, <<"-">>),
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WestVal = get_new_direction_val(Maze, X - 1, Y, Marked, <<"-">>),
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if NorthVal -> { 0, -1 };
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SouthVal -> { 0, 1 };
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EastVal -> { 1, 0 };
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WestVal -> { -1, 0 }
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end.
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get_new_direction_val(Maze, X, Y, Marked, DesiredChar)
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-> Key = { X, Y },
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HasKey = dict:is_key(Key, Marked),
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if HasKey ->
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IsMarked = dict:fetch(Key, Marked),
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if IsMarked == 1 -> false;
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true ->
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Piece = dict:fetch(Key, Maze),
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Piece == DesiredChar
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end;
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true -> false
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end.
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start()
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-> { ok, File } = file:read_file("input"),
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InputList = re:split(unicode:characters_to_list(string:chomp(File)), "\n"),
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Maze = map_input(InputList),
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Marked = dict:fold(fun(Key, _Value, Acc) -> dict:store(Key, 0, Acc) end, dict:new(), Maze),
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io:fwrite("~p~n", [trace_maze(Maze, 157, 0, Marked, [], 1, 0, 1)]).
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