diff --git a/2024/18/example.txt b/2024/18/example.txt
new file mode 100644
index 0000000..79c8583
--- /dev/null
+++ b/2024/18/example.txt
@@ -0,0 +1,25 @@
+5,4
+4,2
+4,5
+3,0
+2,1
+6,3
+2,4
+1,5
+0,6
+3,3
+2,6
+5,1
+1,2
+5,5
+2,5
+6,5
+1,4
+0,4
+6,4
+1,1
+6,1
+1,0
+0,5
+1,6
+2,0
diff --git a/2024/18/solution.nix b/2024/18/solution.nix
new file mode 100644
index 0000000..65897eb
--- /dev/null
+++ b/2024/18/solution.nix
@@ -0,0 +1,52 @@
+{lib, input ? "", my-lib, ...}@pkgs: rec {
+  inherit pkgs;
+  inherit lib;
+  inherit (builtins) elemAt genList elem concatStringsSep;
+  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";
+
+  mkSolution = {size, bytes, input}: rec {
+    inherit size bytes input;
+    walls = lib.sublist 0 bytes (init input);
+    chart = genChart size walls;
+    part1result = dijkstra.toGoal.steps;
+    dijkstra = my-lib.dijkstra {
+      pos = {x = 0; y = 0;};
+      goal = {x = size - 1; y = size - 1;};
+      chart = chart;
+      width = size;
+      height = size;
+    };
+  };
+
+  example = mkSolution {
+    size = 7;
+    bytes = 12;
+    input = lib.readFile ./example.txt;
+  };
+
+  real = mkSolution {
+    size = 71;
+    bytes = 1024;
+    input = input;
+  };
+
+  # not 272, too high
+
+}
diff --git a/2024/flake.lock b/2024/flake.lock
index fa45999..428cf6f 100644
--- a/2024/flake.lock
+++ b/2024/flake.lock
@@ -3,8 +3,8 @@
     "aoc-inputs": {
       "flake": false,
       "locked": {
-        "lastModified": 1734334657,
-        "narHash": "sha256-NjsEC/6Mu+i94YPgK4yN0Y5TxhlWwXK5Ev2UzIkfGZo=",
+        "lastModified": 1734543082,
+        "narHash": "sha256-hU8vRkPOKfQqp34Ffx4INiz3l6HdwGcbfyHgqO4qheM=",
         "path": "/tmp/aoc-inputs",
         "type": "path"
       },
diff --git a/2024/flake.nix b/2024/flake.nix
index 67dfb0b..51a7592 100644
--- a/2024/flake.nix
+++ b/2024/flake.nix
@@ -29,12 +29,16 @@
   |> map (i: let id = lib.fixedWidthNumber 2 i; in {
     name = "day-${id}";
     value = let
-      solution = import ./${id}/solution.nix pkgs;
+      solution = import ./${id}/solution.nix ( pkgs // {
+        my-lib = import ./lib/. pkgs;
+        inherit input;
+      } );
       example = (pkgs.lib.readFile ./${id}/example.txt);
       example2 = (pkgs.lib.readFile ./${id}/example2.txt);
       example3 = (pkgs.lib.readFile ./${id}/example3.txt);
       input = (pkgs.lib.readFile "${aoc-inputs}/${id}");
     in {
+      inherit solution;
       example = solution example;
       example2 = solution example2;
       example3 = solution example3;
diff --git a/2024/lib/default.nix b/2024/lib/default.nix
new file mode 100644
index 0000000..4649f02
--- /dev/null
+++ b/2024/lib/default.nix
@@ -0,0 +1,3 @@
+pkgs: {
+  dijkstra = import ./dijkstra.nix pkgs;
+}
diff --git a/2024/lib/dijkstra.nix b/2024/lib/dijkstra.nix
new file mode 100644
index 0000000..28b32da
--- /dev/null
+++ b/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;
+}