98 lines
2.6 KiB
Nix
98 lines
2.6 KiB
Nix
{lib, ...}: input: rec {
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inherit lib;
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inherit (lib) splitString mod;
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inherit (lib.lists) findFirstIndex imap0;
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inherit (lib.strings) stringToCharacters;
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inherit (builtins) elemAt concatStringsSep length elem filter foldl' concatLists;
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index = i: list: elemAt list i;
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index2d = {x, y}: m: m |> index y |> index x;
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init = let
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parts = splitString "\n\n" input;
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chart = elemAt parts 0 |> splitString "\n" |> map stringToCharacters;
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# ins = elemAt parts 1 |> stringToCharacters |> filter (char: elem char (stringToCharacters "^><v"));
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ins = elemAt parts 1 |> splitString "\n" |> map stringToCharacters;
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width = (elemAt chart 0 |> length) + 1;
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startIndex = elemAt parts 0 |> stringToCharacters |> findFirstIndex (char: char == "@") null;
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in {
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inherit chart ins;
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pos = {
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x = mod startIndex width;
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y = startIndex / width;
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};
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}
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;
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addVec = a: b: {x = a.x + b.x; y = a.y + b.y;};
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objects = {
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wall = "#";
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moveable = "O";
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empty = ".";
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};
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replace2d = {x, y}: updated: chart: let
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newRow = chart |> index y |> replace x updated;
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in
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replace y newRow chart;
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replace = i: updated: list:
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let before = lib.sublist 0 i list;
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after = lib.sublist (i + 1) (builtins.length list - i) list;
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in
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if i < 0 || i > builtins.length list then list else
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before ++ [updated] ++ after;
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strToDir = strDir: {
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x = if strDir == "<" then -1 else if strDir == ">" then 1 else 0;
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y = if strDir == "^" then -1 else if strDir == "v" then 1 else 0;
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};
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move = {chart, pos, ...}: dir: let
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nextPos = addVec pos dir;
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atPos = chart |> index2d pos;
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moved = move {inherit chart; pos = nextPos;} dir;
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in if atPos == objects.wall
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then {
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inherit chart pos;
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moved = false;
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} else if atPos == objects.empty
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then {
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inherit chart pos;
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moved = true;
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} else if !moved.moved
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then {inherit chart pos; moved = false;}
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else {
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moved = true;
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pos = nextPos;
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chart = moved.chart |> replace2d pos objects.empty |> replace2d nextPos atPos;
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};
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chartToStr = chart: chart |> (map (concatStringsSep "")) |> concatStringsSep "\n";
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applyIns = foldl' (c: ins: let
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dir = strToDir ins;
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in move c dir);
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applyInsList = foldl' (chart: ins:
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# evaluate each line of instructions one at a time, to avoid stack overflow.
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let res = applyIns chart ins; in builtins.deepSeq res
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(res)
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);
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result = applyInsList init init.ins;
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getScore = chart: chart
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|> imap0 (y: row: row
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|> imap0 (x: obj:
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if obj == objects.moveable then x + y * 100 else 0
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)
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)
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|> concatLists
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|> foldl' builtins.add 0
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;
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part1result = getScore result.chart;
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}
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