2024 day 15 part 2 in nix

2024/15/example3.txt

@@ -0,0 +1,9 @@
+#######
+#...#.#
+#.....#
+#..OO@#
+#..O..#
+#.....#
+#######
+
+<vv<<^^<<^^

2024/15/solution.nix

@@ -3,7 +3,7 @@
   inherit (lib) splitString mod;
   inherit (lib.lists) findFirstIndex imap0;
   inherit (lib.strings) stringToCharacters;
-  inherit (builtins) elemAt concatStringsSep length elem filter foldl' concatLists;
+  inherit (builtins) elemAt concatStringsSep length elem filter foldl' concatLists floor;
 
   index = i: list: elemAt list i;
   index2d = {x, y}: m: m |> index y |> index x;
@@ -11,7 +11,6 @@
   init = let
     parts = splitString "\n\n" input;
     chart = elemAt parts 0 |> splitString "\n" |> map stringToCharacters;
-    # ins = elemAt parts 1 |> stringToCharacters |> filter (char: elem char (stringToCharacters "^><v"));
     ins = elemAt parts 1 |> splitString "\n" |> map stringToCharacters;
     width = (elemAt chart 0 |> length) + 1;
     startIndex = elemAt parts 0 |> stringToCharacters |> findFirstIndex (char: char == "@") null;
@@ -24,11 +23,13 @@
   }
   ;
 
-  addVec = a: b: {x = a.x + b.x; y = a.y + b.y;};
+  addVec = a: b: {x = a.x or 0 + b.x or 0; y = a.y or 0 + b.y or 0;};
 
   objects = {
     wall = "#";
     moveable = "O";
+    leftedge = "[";
+    rightedge = "]";
     empty = ".";
   };
 
@@ -94,4 +95,70 @@
   ;
 
   part1result = getScore result.chart;
+
+  init2 = {
+    chart = init.chart
+      |> map (map (c: if c == objects.moveable then ["[" "]"]
+      else if c == "@" then ["@" "."] else [c c]))
+      |> map concatLists
+    ;
+    pos = {
+      inherit (init.pos) y;
+      x = init.pos.x * 2;
+    };
+  };
+
+  move2 = dir: {chart, pos, ...}:
+  let
+    nextPos = addVec pos dir;
+    char = chart |> index2d pos;
+    switch = state: state // {chart = state.chart |> replace2d pos objects.empty |> replace2d nextPos char;};
+    moved = move2 dir {inherit chart; pos = nextPos;} |> switch;
+    moved2 = if dir.y == 0 || !moved.moved then moved else if char == objects.leftedge then
+        move2 dir {inherit (moved) chart; pos = addVec pos {x = 1;};}
+      else if char == objects.rightedge then
+        move2 dir {inherit (moved) chart; pos = addVec pos {x = -1;};}
+      else
+        moved;
+  in if char == objects.wall
+  then {
+    inherit chart pos;
+    moved = false;
+  } else if char == objects.empty
+  then {
+    inherit chart pos;
+    moved = true;
+  } else if !moved2.moved
+  then {inherit chart pos; moved = false;}
+  else {
+    moved = true;
+    pos = nextPos;
+    inherit (moved2) chart;
+  }
+  ;
+
+  applyIns2 = foldl' (c: ins: let
+    dir = strToDir ins;
+  in move2 dir c);
+
+  applyInsList2 = foldl' (chart: ins:
+    # evaluate each line of instructions one at a time, to avoid stack overflow.
+    let res = applyIns2 chart ins; in builtins.deepSeq res
+    res
+  );
+
+  result2 = applyInsList2 init2 init.ins;
+
+  getScore2 = chart: chart
+    |> imap0 (y: row: row
+      |> imap0 (x: obj:
+        if obj == objects.leftedge then x + y * 100 else 0
+      )
+    )
+    |> concatLists
+    |> foldl' builtins.add 0
+  ;
+
+  part2result = getScore2 result2.chart;
+
 }

2024/flake.nix

@@ -31,11 +31,11 @@
     value = let
       solution = import ./${id}/solution.nix pkgs;
       example = (pkgs.lib.readFile ./${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 {
       example = solution example;
-      example2 = solution example2;
+      example3 = solution example3;
       real = solution input;
       test = tix.run [
         ./${id}/solution.test.nix