2024 day 18 part 1

2024/lib/default.nix

@@ -0,0 +1,3 @@
+pkgs: {
+  dijkstra = import ./dijkstra.nix pkgs;
+}

2024/lib/dijkstra.nix

@@ -0,0 +1,212 @@
+{lib, pkgs, ...}: {pos, goal, chart, width, height}@init: rec {
+  inherit lib;
+  inherit (lib) splitString mod range;
+  inherit (lib.lists) findFirstIndex imap0;
+  inherit (lib.strings) stringToCharacters;
+  inherit (builtins) elemAt concatStringsSep length elem filter foldl' concatLists floor deepSeq listToAttrs attrValues attrNames mapAttrs hasAttr sort genList;
+
+  index = i: list: if isNull list || i < 0 || i >= length list then null else elemAt list i;
+  index2d = {x, y}: m: m |> index y |> index x;
+
+  chartToStr = chart: chart |> (map (concatStringsSep "")) |> concatStringsSep "\n";
+
+  rotate' = {x, y}: {y = -x; x = y;};
+  rotate = {x, y}: {y = x; x = -y;};
+
+  addVec = a: b: {x = a.x or 0 + b.x or 0; y = a.y or 0 + b.y or 0;};
+  multVec = a: m: {x = a.x or 0 * m; y = a.y or 0 * m;};
+
+
+  dirs = {
+    north = {x = 0; y = -1;};
+    east = {x = 1; y = 0;};
+    south = {x = 0; y = 1;};
+    west = {x = -1; y = 0;};
+  };
+
+  search = {
+    pos,
+    dir,
+    score ? 0,
+  }: let
+    fwd = addVec pos dir;
+  in
+  if
+    elem (index2d fwd init.chart) [null "#"]
+    then {pos = null; dist = null;}
+  else
+  if (isCorner fwd || fwd == init.goal || fwd == init.pos)
+    then {
+      pos = (key fwd);
+      dist = score + 1;
+    }
+  else
+    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))
+  ;
+
+  key = {x, y}: "${toString (y + 1)},${toString (x + 1)}";
+
+  corners = range 0 (init.width - 1) |> map (x:
+    range 0 (init.height - 1) |> map (y: {inherit x y;})
+  )
+  |> concatLists
+  |> filter isCorner
+  |> (nodes: nodes ++ [init.pos init.goal])
+  |> map (pos: {
+    name = key pos;
+    value = ({
+      north = search {inherit pos; dir = dirs.north;};
+      east = search {inherit pos; dir = dirs.east;};
+      south = search {inherit pos; dir = dirs.south;};
+      west = search {inherit pos; dir = dirs.west;};
+    } |> lib.filterAttrs (n: v: !isNull v.pos));
+  })
+  |> listToAttrs;
+
+  notNull = value: !isNull value;
+
+  nodeGraph = graph: pkgs.runCommand "graph" {} ''
+    mkdir -p $out
+    echo 'digraph {
+      ${graph |> mapAttrs (from: edges:
+        edges |> mapAttrs (dir: edge: if isNull edge.pos or null then "" else ''
+          "${from}" -> "${edge.pos}" [label="${dir} ${toString edge.dist}"]
+        '') |> attrValues |> concatStringsSep "\n"
+      ) |> attrValues |> concatStringsSep "\n"}
+    }' > $out/graph.dot
+    cat $out/graph.dot | ${pkgs.graphviz}/bin/dot -Tsvg > $out/graph.svg
+  '';
+
+  graphs = {
+    corners = nodeGraph corners;
+  };
+
+  initScores = {
+    ${key init.pos} = {
+      dir = "east";
+      steps = 0;
+      dist = 0;
+      turns = 0;
+      pos = key init.pos;
+    };
+  };
+
+  getLowest = state: let
+    unvisited = removeAttrs state.scores state.done;
+  in
+    attrValues unvisited |> foldl' (acc: node:
+      if isNull acc.steps then node else
+        if isNull node.steps then acc else
+        if acc.steps < node.steps then acc else node
+    ) {turns = null; steps = null;}
+  ;
+
+  getScores = {done ? [], scores ? initScores}: let
+    prev = getLowest {inherit done scores;};
+  in
+    corners.${prev.pos}
+    |> mapAttrs (dir: edge: let
+      turns = if prev.dir == dir then prev.turns else prev.turns + 1;
+      existing = scores.${edge.pos} or null;
+      steps = prev.steps + edge.dist;
+      # can't evaluate same turns
+      # because we don't know where we will turn next.
+      sameSteps = notNull existing
+        && existing.steps == steps
+      ;
+      isBetter = isNull existing ||
+        (existing.steps > steps);
+      newScore = {
+        inherit steps dir turns;
+        inherit (edge) pos dist;
+        prev = prev.pos;
+      };
+    in {
+      name = edge.pos;
+      value = if sameSteps then
+        existing // {alt = newScore;}
+      else if isBetter
+      then newScore
+      else existing
+      ;
+    })
+    |> attrValues
+    |> listToAttrs
+    |> (newScores: {
+      scores = scores // newScores;
+      done = done ++ [prev.pos];
+    })
+  ;
+
+  fastest = goal: s: let
+    next = getScores s;
+  in if elem (key goal) (next.done) then next else fastest goal next;
+
+  pathScore = steps: turns: steps + turns * 1000;
+
+  toGoal = (fastest init.goal {}).scores.${key init.goal};
+
+  part1result = pathScore toGoal.steps toGoal.turns;
+
+# PART 2
+
+  # WIP:
+  # go through the path, add each pos to visited
+  # if point has alt,
+  # TODO: and the alt turns add up to the correct path.
+  # find points on that path.
+  # add length of filtered alt, (-1 for the overlap at end?).
+  # add alt to visited.
+  pathToList = scores: {pos ? key init.goal, visited ? []}:
+  let
+    res = scores.${pos};
+    prevPath = if res ? prev
+      then pathToList scores {pos = res.prev; visited = visited;}
+      else {path = []; visited = [pos];};
+    a = pathToList scores {pos = res.alt.prev; visited = visited ++ prevPath.visited;};
+    altPath = if res ? alt
+      then {path = [thisAltSpot] ++ a.path; inherit (a) visited;}
+      else {path = []; visited = [];}
+    ;
+
+    thisSpot = {inherit (res) pos steps turns dir dist;
+      # alt = altPath.path;
+    };
+    thisAltSpot = {inherit (res.alt) pos steps turns dir dist;
+      alt = [];
+    };
+
+  in {
+    visited = [pos] ++ prevPath.visited ++ altPath.visited;
+    path =
+      if elem pos visited then [] else
+      [thisSpot]
+      ++
+      prevPath.path
+    ;
+  };
+
+  cornerScores = fastest init.goal {};
+
+  addDist = foldl' (acc: {dist,alt,dir,...}:
+    acc + dist + (if addDist alt == 1 then 0 else (addDist alt) - 2)
+  ) 1;
+
+  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 "#"
+    else if elem (key {inherit x y;}) (map ({pos,...}: pos) path) then "O"
+    else "."
+  ) size) size;
+}