23 lines
1.2 KiB
Nix
23 lines
1.2 KiB
Nix
{ lib, utils, ... }:
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with lib;
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with builtins;
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with utils;
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let
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input_parts = reSplit "\n\n" (readFile ./input);
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orders = map (reSplit "\\|") (reSplit "\n" (head input_parts));
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records = map (reSplit ",") (init (reSplit "\n" (last input_parts)));
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# defines mapping of number -> [ blocked numbers that can't come after. Sorted for readability. ]
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blocking = mapAttrs (_: v: map head v |> naturalSort |> unique ) (groupBy last orders);
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isValid = r: all (i: let p = elemAt r i; in !hasAttr p blocking || (intersectLists (drop (i + 1) r ) blocking."${p}") == [] ) (listRange r);
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sortRecord = r: if r == [] then [] else (let
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h = head r;
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intersect = if !hasAttr h blocking then [] else intersectLists (tail r ) blocking."${h}";
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# Idea: check first element, and pull all "bad" elements ahead. If there is no "bad" elements, take the head and go down.
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in if intersect == [] then [h] ++ sortRecord (tail r) else sortRecord (intersect ++ [ h ] ++ (removeAll intersect (tail r))) );
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in {
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part1 = filter isValid records |> map elemAtMid |> listSumWith toInt;
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part2 = filter (invert isValid) records |> map sortRecord |> map elemAtMid |> listSumWith toInt;
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}
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