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97 lines
2.7 KiB
97 lines
2.7 KiB
-module(day9).
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-export([solve/1]).
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solve(Input) ->
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%#{visited := Visited} = EndState = fold_moves(Input, fun simulate/2, State),
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{simulate_rope(Input, 1), simulate_rope(Input, 9)}.
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make_rope(Length) ->
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Rope0 = make_head(),
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Rope1 = add_knots(Rope0, Length),
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add_trace(Rope1).
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simulate_rope(Input, Length) ->
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{RopeFn, RopeState} = make_rope(Length),
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{Visited, _RopeState} = fold_moves(Input, RopeFn, RopeState),
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map_size(Visited).
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make_head() ->
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{
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fun(Move, [Pos]) ->
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[vec_add(Move, Pos)]
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end,
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[{0, 0}]
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}.
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add_knot({HeadFn, Head0}) ->
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{
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fun(Move, [TailPos|HeadState]) ->
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[HeadPosNew|_] = HeadStateNew = HeadFn(Move, HeadState),
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[chase_tail(HeadPosNew, TailPos) | HeadStateNew]
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end,
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[{0,0}|Head0]
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}.
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add_knots(Stream, 0) -> Stream;
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add_knots(Stream, N) -> add_knots(add_knot(Stream), N-1).
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add_trace({SimFn, Sim0}) ->
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{
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fun(Move, {Visited, SimAccIn}) ->
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[Pos | _] = SimAccOut = SimFn(Move, SimAccIn),
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{Visited#{Pos => []}, SimAccOut}
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end,
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{#{}, Sim0}
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}.
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simulate(Move, #{head := Head, tail := Tail, visited := Visited}) ->
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NewHead = vec_add(Head, Move),
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NewTail = chase_tail(NewHead, Tail),
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NewVisited = Visited#{NewTail => []},
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#{head => NewHead, tail => NewTail, visited => NewVisited}.
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chase_tail(Head, Tail) ->
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Diff = vec_sub(Head, Tail),
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case vec_norm(Diff) of
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Diff -> Tail;
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Norm -> vec_add(Norm, Tail)
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end.
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fold_instructions(<<Letter, $\s, RestIn/binary>>, Fun, Acc) ->
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{Count, RestOut} = parse_int(RestIn, 0),
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Direction =
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case Letter of
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$U -> up;
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$D -> down;
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$L -> left;
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$R -> right
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end,
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fold_instructions(RestOut, Fun, Fun({Direction, Count}, Acc));
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fold_instructions(<<$\n, Rest/binary>>, Fun, Acc) -> fold_instructions(Rest, Fun, Acc);
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fold_instructions(<<>>, _Fun, Acc) -> Acc.
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fold_moves(Stream, Fun, Acc) -> element(2, fold_instructions(Stream, fun per_move/2, {Fun, Acc})).
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per_move({Direction, Count}, {Fun, Acc}) -> {Fun, per_move0(direction_vec(Direction), Count, Fun, Acc)}.
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per_move0(_Move, 0, _Fun, Acc) -> Acc;
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per_move0(Move, Count, Fun, Acc) -> per_move0(Move, Count-1, Fun, Fun(Move, Acc)).
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direction_vec(up) -> {0, 1};
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direction_vec(down) -> {0, -1};
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direction_vec(left) -> {-1, 0};
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direction_vec(right) -> {1, 0}.
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vec_add({X1, Y1}, {X2, Y2}) -> {X1+X2, Y1+Y2}.
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vec_sub({X1, Y1}, {X2, Y2}) -> {X1-X2, Y1-Y2}.
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vec_norm({X, Y}) -> {norm(X), norm(Y)}.
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norm(X) when X > 0 -> 1;
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norm(X) when X < 0 -> -1;
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norm(0) -> 0.
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parse_int(<<Char, Rest/binary>>, Acc) when Char >= $0 andalso Char =< $9 -> parse_int(Rest, Acc*10+(Char - $0));
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parse_int(Rest, Acc) -> {Acc, Rest}.
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