63 lines
1.5 KiB
Nix
63 lines
1.5 KiB
Nix
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{lib, ...}: input: rec {
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content = lib.trim input;
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chart = content
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|> lib.strings.splitString "\n"
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|> map (lib.strings.splitString "")
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|> map (line: lib.sublist 1 (builtins.length line - 2) line)
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;
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startingPos = let
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xs = map (lib.lists.findFirstIndex (char: char == "^") null) chart;
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y = lib.lists.findFirstIndex (x: !isNull x) null xs;
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x = builtins.elemAt xs y;
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in
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{inherit x y;}
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;
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posToString = {x, y}: "${toString x},${toString y}";
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addVec = a: b: {x = a.x + b.x; y = a.y + b.y;};
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index = i: list: builtins.elemAt list i;
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getChar = {x, y}: chart
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|> index y
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|> index x
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;
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height = builtins.length chart;
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width = chart |> index 0 |> builtins.length;
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progress = {visited ? {}, pos, dir, ...}: let
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nextChar = getChar (addVec pos dir);
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newDir = if nextChar == "#" then rotate dir else dir;
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newPos = addVec pos newDir;
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fwd = addVec pos dir;
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in
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{
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visited = visited // {${posToString pos} = true;};
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exited = fwd.y >= height || fwd.x >= width || fwd.y < 0 || fwd.x < 0;
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pos = newPos;
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dir = newDir;
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};
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rotate = {x, y}: {x = -y; y = x;};
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startingDir = {x = 0; y = -1;};
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getVisits = {pos ? startingPos, dir ? startingDir, visited ? {}, ...}:
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let
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nextStep = progress {inherit pos dir visited;};
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in if nextStep.exited then visited else getVisits nextStep;
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part1result = getVisits {}
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|> builtins.attrNames
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|> builtins.length
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# the last position
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|> (v: v + 1)
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;
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}
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