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2024 day 18 part 2

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Tristan 2024-12-18 23:12:50 +00:00
parent 5467ea9393
commit 5d8d809844
2 changed files with 53 additions and 28 deletions
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49
2024/lib/dijkstra.nix
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@ -1,4 +1,4 @@
{lib, pkgs, ...}: {pos, goal, chart, width, height}@init: rec {
{lib, pkgs, ...}: init: rec {
inherit lib;
inherit (lib) splitString mod range;
inherit (lib.lists) findFirstIndex imap0;
@ -44,14 +44,17 @@
search {pos = fwd; inherit dir; score = score + 1;}
;
isCorner = pos: index2d pos init.chart == "." &&
(dirs
|> mapAttrs (name: dir: let n = addVec pos dir; in index2d n init.chart == ".")
|> ({north, east, south, west}:
north && east || east && south || south && west || west && north))
isCorner = pos: index2d pos init.chart == "." # &&
# (dirs
# |> mapAttrs (name: dir: let n = addVec pos dir; in index2d n init.chart == ".")
# |> ({north, east, south, west}:
# north && east || east && south || south && west || west && north))
;
key = {x, y}: "${toString (y + 1)},${toString (x + 1)}";
key = {x, y}:
"${toString x},${toString y}";
# gives locations like vim cursor indicator
#"${toString (y + 1)},${toString (x + 1)}";
corners = range 0 (init.width - 1) |> map (x:
range 0 (init.height - 1) |> map (y: {inherit x y;})
@ -105,12 +108,14 @@
if isNull acc.steps then node else
if isNull node.steps then acc else
if acc.steps < node.steps then acc else node
) {turns = null; steps = null;}
) {turns = null; steps = null; pos = null;}
;
getScores = {done ? [], scores ? initScores}: let
prev = getLowest {inherit done scores;};
in
if isNull prev.pos then {inherit done scores; impossible = true;}
else
corners.${prev.pos}
|> mapAttrs (dir: edge: let
turns = if prev.dir == dir then prev.turns else prev.turns + 1;
@ -145,13 +150,18 @@
})
;
fastest = goal: s: let
getFastest = goal: s: let
next = getScores s;
in if elem (key goal) (next.done) then next else fastest goal next;
in if next.impossible or false || elem (key goal) (next.done)
then next
else getFastest goal next;
pathScore = steps: turns: steps + turns * 1000;
toGoal = (fastest init.goal {}).scores.${key init.goal};
isImpossible = (getFastest init.goal {}).impossible or false;
fastestTo = (getFastest init.goal {}).scores;
toGoal = fastestTo.${key init.goal};
part1result = pathScore toGoal.steps toGoal.turns;
@ -193,20 +203,13 @@
;
};
cornerScores = fastest init.goal {};
cornerScores = getFastest init.goal {};
addDist = foldl' (acc: {dist,alt,dir,...}:
acc + dist + (if addDist alt == 1 then 0 else (addDist alt) - 2)
) 1;
path = (pathToList cornerScores.scores {}).path;
part1path = (pathToList cornerScores.scores {});
# not 520, too high
part2resultWrong = addDist part1path.path;
genChart = size: walls: path: genList (y: genList (x:
if elem {inherit x y;} walls then "#"
pathChart = genList (y: genList (x:
if index2d {inherit x y;} init.chart == "#" then "#"
else if elem (key {inherit x y;}) (map ({pos,...}: pos) path) then "O"
else "."
) size) size;
) init.width) init.height;
}