2024 day 8 part 2

2024/08/solution.nix

@@ -1,15 +1,19 @@
-{lib, ...}: let
+{lib, ...}: input: let
+
+  abs = n: if n > 0 then n else -n;
 
   addVec = a: b: {x = a.x + b.x; y = a.y + b.y;};
   subVec = a: b: {x = a.x - b.x; y = a.y - b.y;};
+  multVec = m: vec: {x = vec.x * m; y = vec.y * m;};
+  modVec = m: vec: {x = lib.mod vec.x m; y = lib.mod vec.y m;};
 
   toCharList = builtins.foldl'
     ({y, x, chars}: char:
       if char == "." || char == "#" then {inherit y; x = x + 1; inherit chars;}
-      else if char == "\n" then {y = y + 1; x = 1; inherit chars;}
+      else if char == "\n" then {y = y + 1; x = 0; inherit chars;}
       else {inherit y; x = x + 1; chars = chars ++ [{inherit x y char;}];}
     )
-    {y = 1; x = 1; chars = [];} # yeah starting at 1,1 what you gonna do about it
+    {y = 0; x = 0; chars = [];}
   ;
 
   toNodes = {chars, ...}@amap: amap // {
@@ -25,17 +29,44 @@
   };
 
   getUniqueNodes = amap: let
-    size = amap.x;
+    # assumes width == height ¯\_(ツ)_/¯
+    size = assert amap.x == amap.y + 1; amap.x;
   in amap.nodes
       |> lib.concatLists
-      |> builtins.filter ({x, y}: x > 0 && y > 0 && x < size && y < size)
+      |> builtins.filter ({x, y}: x >= 0 && y >= 0 && x < size && y < size)
       |> lib.unique
   ;
 
-in {
+  cut = i: list: lib.sublist i (builtins.length list) list;
-  inherit addVec subVec toCharList toNodes;
 
-  part1result = s: s
+  toDeltas = {chars, ...}@amap: amap // {
+    deltas = chars |> lib.imap0 (i: antenna: {
+      pos = {inherit (antenna) x y;};
+      deltas = chars |> cut i |> builtins.foldl' (acc: antenna2:
+        if antenna == antenna2 then acc
+        else if antenna.char != antenna2.char then acc
+        else let
+          delta = subVec antenna antenna2;
+        in acc ++ [delta]
+      ) [];
+    });
+  };
+
+  deltaToNodes = size: {pos, delta}:
+    builtins.genList
+      (i: delta |> multVec i |> subVec (minNode size pos delta))
+      (size / (lib.max (abs delta.x) (abs delta.y)) + 1)
+    |> builtins.filter ({x, y}: x >= 0 && y >= 0 && x < size && y < size)
+  ;
+
+  minNode = size: pos: delta: let sub = addVec pos delta; in
+    if sub.x < 0 || sub.y < 0 || sub.x >= size || sub.y >= size then pos
+    else minNode size sub delta;
+
+in {
+  inherit addVec subVec toCharList toNodes toDeltas multVec modVec deltaToNodes minNode;
+
+  part1result = input
     |> lib.trim
     |> lib.stringToCharacters
     |> toCharList
@@ -44,5 +75,21 @@ in {
     |> builtins.length
   ;
 
+  part2result = input
+    |> lib.trim
+    |> lib.stringToCharacters
+    |> toCharList
+    |> toDeltas
+    |> ({deltas,x,...}: deltas |> map (antenna:
+      antenna.deltas |> map (delta: deltaToNodes x {
+        inherit delta;
+        inherit (antenna) pos;
+      }
+    )))
+    |> lib.concatLists
+    |> lib.concatLists
+    |> lib.unique
+    |> builtins.length
+  ;
 
 }

2024/08/solution.test.nix

@@ -1,9 +1,34 @@
 {describe, it, ...}:
 let
   pkgs = import <nixpkgs> {};
+  lib = pkgs.lib;
   solution = import ./solution.nix pkgs;
   exampleInput = pkgs.lib.readFile ./example;
   sample1Input = pkgs.lib.readFile ./sample1;
+
+  charmap = {
+    chars = [
+      { char = "0"; x = 8; y = 1; }
+      { char = "0"; x = 5; y = 2; }
+      { char = "0"; x = 7; y = 3; }
+      { char = "0"; x = 4; y = 4; }
+      { char = "A"; x = 6; y = 5; }
+      { char = "A"; x = 8; y = 8; }
+      { char = "A"; x = 9; y = 9; }
+    ];
+    x = 12;
+    y = 11;
+  };
+
+  deltamap = [
+    { deltas = [ { x = 3; y = -1; } { x = 1; y = -2; } { x = 4; y = -3; } ]; pos = { x = 8; y = 1; }; }
+    { deltas = [ { x = -2; y = -1; } { x = 1; y = -2; } ]; pos = { x = 5; y = 2; }; }
+    { deltas = [ { x = 3; y = -1; } ]; pos = { x = 7; y = 3; }; }
+    { deltas = []; pos = { x = 4; y = 4; }; }
+    { deltas = [ { x = -2; y = -3; } { x = -3; y = -4; } ]; pos = { x = 6; y = 5; }; }
+    { deltas = [ { x = -1; y = -1; } ]; pos = { x = 8; y = 8; }; }
+    { deltas = []; pos = { x = 9; y = 9; }; }
+  ];
 in [
   (describe "part 1" [
     (it "get's the answer with example input" {
@@ -23,4 +48,43 @@ in [
       expected = {x = 3; y = 1;};
     })
   ])
+  (describe "part 2" [
+    (it "get's char list" {
+      actual = exampleInput |> lib.trim |> lib.stringToCharacters
+        |> solution.toCharList;
+      expected = charmap;
+    })
+    (it "gets deltas" {
+      actual = (charmap |> solution.toDeltas).deltas;
+      expected = deltamap;
+    })
+    (it "gets nodes" {
+      /*
+        .#...
+        .....
+        ..A..
+        .....
+        ...#.
+      */
+      actual = solution.deltaToNodes 5 {pos = {x=2;y=2;}; delta = {x=-1;y=-2;};};
+      expected = [
+        {x = 1; y = 0;}
+        {x = 2; y = 2;}
+        {x = 3; y = 4;}
+      ];
+    })
+    (it "gets min node" {
+      # .....
+      # #....
+      # .#...
+      # ..A..
+      # ...#.
+      actual = solution.minNode 5 {x = 2; y = 3;} {x = -1; y = -1;};
+      expected = {x = 0; y = 1;};
+    })
+    (it "gets result" {
+      actual = solution.part2result exampleInput;
+      expected = 34;
+    })
+  ])
 ]

2024/flake.nix

@@ -16,18 +16,6 @@
       input = (pkgs.lib.readFile ./06/input.txt);
     in {
       example = (solution example);
-      sample1 = (solution ''
-.#.
-..#
-#^.
-.#.'');
-      sample2 = (solution ''
-.#....
-......
-.....#
-#.....
-..#.#.
-...^..'');
       real = (solution input);
     };
 
@@ -48,8 +36,8 @@
       example = (pkgs.lib.readFile ./08/example);
       input = (pkgs.lib.readFile ./08/input);
     in {
-      solution = solution;
+      example = solution example;
-      part1result = solution.part1result input;
+      real = solution input;
       test = tix.run [
         ./08/solution.test.nix
       ];