2024 day 3 part 2

2024/03/solution.nix

@@ -15,4 +15,44 @@
 
   part1result = content |> muls |> mul;
 
+  conditionsAndMuls = memory: let
+    mulMatcher = ''mul\(([0-9]{0,3}),([0-9]{0,3})\)'';
+    conditionMatcher = ''(do|don't)\(\)'';
+  in memory
+    |> builtins.split "${mulMatcher}|${conditionMatcher}"
+    |> builtins.filter builtins.isList
+    |> map toInstruction
+  ;
+
+  toInstruction = matches: let
+    elem = builtins.elemAt matches;
+    numOrZero = v: if isNull v
+      then 0
+      else lib.strings.toInt v;
+  in {
+    cmd = let todo = elem 2; in
+      if isNull todo then "mul" else todo;
+    a = numOrZero (elem 0);
+    b = numOrZero (elem 1);
+  };
+
+  conditionalMul = builtins.foldl'
+    ({mul, acc}: n: {
+      acc = acc + mul * n.a * n.b;
+      mul = if n.cmd == "do" then 1
+        else if n.cmd == "don't" then 0
+        else mul;
+    })
+    {
+      mul = 1;
+      acc = 0;
+    }
+  ;
+
+  part2result = content
+    |> conditionsAndMuls
+    |> conditionalMul
+    |> (r: r.acc)
+  ;
+
 }

2024/03/solution.test.nix

@@ -12,6 +12,17 @@ let
         ["11" "8"]
         ["8"  "5"]
       ];
+  td2 = ''
+    xmul(2,4)&mul[3,7]!^don't()_mul(5,5)+mul(32,64](mul(11,8)undo()?mul(8,5))
+  '';
+  ti2 = [
+    { a = 2; b = 4; cmd = "mul"; }
+    { a = 0; b = 0; cmd = "don't"; }
+    { a = 5; b = 5; cmd = "mul"; }
+    { a = 11; b = 8; cmd = "mul"; }
+    { a = 0; b = 0; cmd = "do"; }
+    { a = 8; b = 5; cmd = "mul"; }
+  ];
 in [
   (describe "part 1" [
     (it "gets content" {
@@ -31,4 +42,14 @@ in [
       expected = 161;
     })
   ])
+  (describe "part 2" [
+    (it "gets all instructions" {
+      actual = example.conditionsAndMuls td2;
+      expected = ti2;
+    })
+    (it "conditional multiplies" {
+      actual = (example.conditionalMul ti2).acc;
+      expected = 48;
+    })
+  ])
 ]