2024 day 16 struggles

2024/16/solution.nix

@@ -3,7 +3,7 @@
   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;
+  inherit (builtins) elemAt concatStringsSep length elem filter foldl' concatLists floor deepSeq listToAttrs attrValues attrNames mapAttrs hasAttr sort;
 
   index = i: list: elemAt list i;
   index2d = {x, y}: m: m |> index y |> index x;
@@ -52,18 +52,18 @@
   in
   if
     index2d fwd init.chart == "#"
-    then null
+    then {pos = null; dist = null;}
   else
-  if (isNode fwd || fwd == init.goal || fwd == init.pos)
+  if (isCorner fwd || fwd == init.goal || fwd == init.pos)
     then {
-      name = (key fwd);
-      value = score + 1;
+      pos = (key fwd);
+      dist = score + 1;
     }
   else
     search {pos = fwd; inherit dir; score = score + 1;}
   ;
 
-  isNode = pos: index2d pos init.chart == "." &&
+  isCorner = pos: index2d pos init.chart == "." &&
     (dirs
     |> mapAttrs (name: dir: let n = addVec pos dir; in index2d n init.chart == ".")
     |> ({north, east, south, west}:
@@ -72,126 +72,192 @@
 
   key = {x, y}: "${toString (y + 1)},${toString (x + 1)}";
 
-  nodes = range 1 (init.width - 3) |> map (x:
+  corners = range 1 (init.width - 3) |> map (x:
     range 1 (init.height - 3) |> map (y: {inherit x y;})
   )
   |> concatLists
-  |> filter isNode
+  |> filter isCorner
   |> (nodes: nodes ++ [init.pos init.goal])
   |> map (pos: {
     name = key pos;
-    value = {
+    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);
+    } |> lib.filterAttrs (n: v: !isNull v.pos)) // {
+      # pos = key pos;
+    };
   })
   |> listToAttrs;
 
-  graph = pkgs.runCommand "graph" {} ''
+  notNull = value: !isNull value;
+
+###### collecting continuous corners, doesn't work.
+  countDirs = {north ? null, south ? null, east ? null, west ? null, ...}:
+    [north south east west]
+      |> filter (dir: notNull dir && notNull dir.pos)
+      |> length
+  ;
+
+  continue = prev: {dirs, dist ? 0}: let
+    dir = if prev == "north" then "south" else
+      if prev == "south" then "north" else
+      if prev == "west" then "east" else
+      if prev == "east" then "west" else
+        throw "${toString prev} is not a direction!";
+    prevEdge = dirs.${dir};
+  in
+    dirs |> lib.attrsToList |> lib.findFirst (
+      {name, value}: !(name == dir) && !(isDead value)
+    ) null
+    |> (res: res.value // {dir = res.name;})
+    |> (next: let
+      nextCorner = corners.${next.pos};
+    in
+    if isDead nextCorner || isDeadend nextCorner then null else
+    if isNode nextCorner
+      then next // {dist = next.dist + dist + prevEdge.dist + 1000;}
+      else continue next.dir {
+        dirs = nextCorner;
+        dist = dist + prevEdge.dist + 1000;
+      }
+    )
+  ;
+
+  isDead = corner: corner.pos or null == null;
+
+  isNode = corner: let c = countDirs corner; in isTerminal corner || c > 2 || c == 1;
+  isTerminal = corner: corner.pos == key init.goal || corner.pos == key init.pos;
+  isDeadend = corner: let c = countDirs corner; in c == 1;
+
+  nodes = corners |> mapAttrs (start: corner:
+    joinNodes corner
+  );
+
+  joinNodes = corner:
+    corner |> mapAttrs (dir: next:
+      if isDead next || isDeadend next
+        then null
+      else if !isNode corners.${next.pos}
+        then continue dir {dirs = corners.${next.pos};}
+      else
+        next // {inherit dir;})
+    |> lib.filterAttrs (n: v: notNull v)
+  ;
+########
+
+  nodeGraph = graph: pkgs.runCommand "graph" {} ''
     mkdir -p $out
     echo 'digraph {
-      ${nodes |> mapAttrs (from: tos:
-        tos |> mapAttrs (dir: edge: if isNull edge then "" else ''
-          "${from}" -> "${edge.name}" [label="${dir} ${toString edge.value}"]
+      ${graph |> mapAttrs (from: edges:
+        edges |> mapAttrs (dir: edge: if isNull edge.pos or null then "" else ''
+          "${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
   '';
 
-  getPath = {
-    pos ? key init.pos
-  , goal
-  , dir ? "east"
-  , score ? 0
-  , hist ? []
-  , acc ? {}
-  }: let
-    node = nodes.${pos};
-  in attrNames node |> foldl' (best: edgedir:
-  lib.traceSeq acc 
-  (let
-    newHist = hist ++ [edge.name value];
-    edge = node.${edgedir};
-    turnCost = if edgedir == dir then 0 else 1000;
-    value = edge.value + turnCost;
-    newScore = score + value;
-  in
-    if isNull edge || elem edge.name hist || (hasAttr "score" best && newScore > best.score) then best else
-    if edge.name == goal && (hasAttr "score" best -> newScore < best.score) then
-      ({score = newScore;})
-    else
-      getPath {
-        pos = edge.name;
-        dir = edgedir;
-        score = newScore;
-        hist = newHist;
-        acc = best;
-        inherit goal;
-      }
-  )) acc;
+  graphs = {
+    corners = nodeGraph corners;
+    nodes = nodeGraph nodes;
+  };
 
   initScores = {
-    scores = mapAttrs (n: v:
-      if n == key init.pos then {dir = "east"; score = 0; pos = n;}
-      else {dir = null; score = null; pos = n;}
-    ) nodes;
-    done = [];
+    ${key init.pos} = {
+      dir = "east";
+      steps = 0;
+      turns = 0;
+      pos = key init.pos;
+    };
   };
 
-  getScores = state: let
+  getLowest = state: let
     unvisited = removeAttrs state.scores state.done;
-    top = attrValues unvisited |> foldl' (acc: node:
-      if isNull acc.score then node else
-        if isNull node.score then acc else
-        if acc.score < node.score then acc else node
-    ) {score = null;};
   in
-    nodes.${top.pos}
-    |> mapAttrs (dir: {name, value}: let
-      turnCost = if top.dir == dir then 0 else 1000;
-      existing = state.scores.${name};
-      score = top.score + value + turnCost;
-      isBetter = isNull existing.score || existing.score > score;
-    in {
-      inherit name;
-      value = if elem name state.done || !isBetter then existing else {
-        inherit dir score;
-        pos = name;
+    attrValues unvisited |> foldl' (acc: node:
+      if isNull acc.turns then node else
+        if isNull node.turns then acc else
+        if acc.turns < node.turns 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;
+      sameSteps = notNull existing
+        && existing.steps == steps
+        # && turns == existing.turns
+      ;
+      isBetter = isNull existing ||
+        (existing.steps > steps);
+      newScore = {
+        inherit steps dir turns;
+        inherit (edge) pos;
+        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 = state.scores // newScores;
-      done = state.done ++ [top.pos];
+      scores = scores // newScores;
+      done = done ++ [prev.pos];
     })
   ;
 
-  getPriority = {scores, done}: scores
-    |> lib.attrsToList
-    |> filter ({name, ...}: !elem name done)
-    |> filter ({value, ...}: !isNull value.score)
-    |> sortQueue
-  ;
-
-  lessThan = a: b: isNull a || isNull b || a < b;
-
-  sortQueue = q: q
-    |> builtins.sort (a: b: lessThan a.value.score b.value.score)
-    # |> (q: lib.traceSeq (map (v: v.value.score) q) q)
-    |> map ({name, value}: {
-      pos = name;
-      inherit (value) dir score;
-    })
-  ;
-
-  fastest = s: let
+  fastest = goal: s: let
     next = getScores s;
-  in if elem (key init.goal) next.done then next else fastest next;
+  in if elem (key goal) (next.done) then next else fastest goal next;
+
+  pathScore = steps: turns: steps + turns * 1000;
+
+  toGoal = (fastest init.goal {}).scores.${key init.goal};
+
+  part1result = pathScore toGoal.steps toGoal.turns;
+
+# PART 2
+
+  # WIP:
+  # go through the path, add each pos to visited
+  # if point has alt, find points on that path not visited yet.
+  # add length of filtered alt, (-1 for the overlap at end?).
+  # add alt to visited.
+  pathToList = scores: pos:
+  let
+    res = scores.${pos};
+    prevPath = if res ? prev then pathToList scores res.prev else [];
+    fullaltPath = pathToList scores res.alt.prev;
+    joinIndex = findFirstIndex ({pos,...}: !elem pos (map ({pos, ...}: pos) prevPath)) null fullaltPath;
+    altPath = lib.sublist (joinIndex - 1) (length fullaltPath) fullaltPath;
+
+    thisSpot = {inherit (res) pos steps turns dir; };
+
+  in
+  prevPath
+  ++
+  [(thisSpot // {
+    alt = if res ? alt then altPath ++ [thisSpot] else null;
+  })]
+  ;
+
+  cornerScores = fastest init.goal {};
+
+  part1path = (pathToList cornerScores.scores (key init.goal));
 
-  part1result = (fastest initScores).scores.${key init.goal};
 
 }

2024/result

@@ -1 +0,0 @@
-/nix/store/3dxw74x2scq38j9m84r6m3iq320npwn4-graph