aoc/2024/18/solution.nix
2024-12-18 23:12:50 +00:00

75 lines
1.9 KiB
Nix

{lib, input ? "", my-lib, ...}@pkgs: rec {
inherit pkgs;
inherit lib;
inherit my-lib;
inherit (builtins) elemAt genList elem concatStringsSep length;
inherit (lib) splitString;
inherit (lib.strings) toIntBase10;
init = input: input |> lib.trim
|> splitString "\n"
|> map (line: let c = splitString "," line; in {
x = elemAt c 0 |> toIntBase10;
y = elemAt c 1 |> toIntBase10;
})
;
genChart = size: coords: genList (y: genList (x:
if x == 0 && y == 0 then "S" else
if x == size - 1 && y == size - 1 then "E" else
if elem {inherit x y;} coords then "#" else "."
) size) size;
chartToStr = chart: chart |> (map (concatStringsSep "")) |> concatStringsSep "\n";
inherit (my-lib.dijkstra {}) key;
mkSolution = {size, bytes, input}: rec {
inherit size bytes input;
walls = init input;
part1result = p1Dijkstra.toGoal.steps;
p1Dijkstra = searchAfterBytes 12;
searchAfterBytes = bytes: let
walls = lib.sublist 0 bytes (init input);
chart = genChart size walls;
in my-lib.dijkstra {
pos = {x = 0; y = 0;};
goal = {x = size - 1; y = size - 1;};
chart = chart;
width = size;
height = size;
};
findFirst = bytes: prevPath: let
dijkstra = lib.traceSeq "retracing after ${toString bytes} with ${key wall}" (searchAfterBytes bytes);
wall = elemAt walls (bytes - 1);
wallCollides = elem (key wall) (map ({pos,...}: pos) prevPath);
in if !wallCollides
then findFirst (bytes + 1) prevPath
else
if dijkstra.isImpossible
then key wall
else
findFirst (bytes + 1) dijkstra.path;
part2result = findFirst bytes p1Dijkstra.path;
};
example = mkSolution {
size = 7;
bytes = 12;
input = lib.readFile ./example.txt;
};
real = mkSolution {
size = 71;
bytes = 1024;
input = input;
};
# not 272, too high
}