43 lines
1.3 KiB
Erlang
43 lines
1.3 KiB
Erlang
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-module(day3).
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-export([start/0]).
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next_largest_square(Target)
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-> recurse_next_largest_square(1, Target).
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recurse_next_largest_square(X, Target)
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when (X rem 2) =/= 0, (X*X) >= Target -> X;
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recurse_next_largest_square(X, Target)
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-> recurse_next_largest_square(X+1, Target).
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position_in_outer_shell(Square, Target)
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-> PreviousSquare = (Square - 2) * (Square - 2),
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Target - PreviousSquare.
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position_on_side(Position, Square)
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when Position == 0 -> Square - 1;
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position_on_side(_Position, Square)
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when Square == 1 -> 1;
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position_on_side(Position, Square)
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-> Offset = Position rem (Square - 1),
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if Offset == 0 -> Square - 1;
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true -> Offset end.
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distance_to_center(Position, Square)
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-> Center = Square div 2,
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VertOffset = abs(Center - Position),
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Center + VertOffset.
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find_distance(Target)
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-> Square = next_largest_square(Target),
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Position = position_in_outer_shell(Square, Target),
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Index = position_on_side(Position, Square),
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distance_to_center(Index, Square).
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start()
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-> io:fwrite("~B ~B~n", [1, find_distance(1)]),
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io:fwrite("~B ~B~n", [12, find_distance(12)]),
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io:fwrite("~B ~B~n", [23, find_distance(23)]),
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io:fwrite("~B ~B~n", [1024, find_distance(1024)]),
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io:fwrite("~B ~B~n", [368078, find_distance(368078)]),
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io:fwrite("https://oeis.org/A141481/b141481.txt~n").
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