my splitStringByLen function was extremely slow, and lists/iterating lists is slow in general so cahnge to splitByLen make old version 60% faster, and a version without the intermediate loop it is 4s

2025/day_2.nix

@@ -30,11 +30,12 @@ let
     str:
     let
       strLen = stringLength str;
-      splits = reverseList (genList (i: i + 1) strLen);
+      maxSplit = strLen / 2;  # Only check up to half length since it must repeat at least twice
+      splits = genList (i: i + 1) maxSplit;
     in
     any (
       split:
-      if split < strLen && mod strLen split == 0 then
+      if mod strLen split == 0 then
         let
           parts = splitStringByLength str split;
         in
@@ -51,7 +52,7 @@ let
     let
       invalidIds = flatten (
         map (
-          range: (reduce (invalidIds: id: invalidIds ++ (if badIdFunc id then [ id ] else [ ])) [ ] range)
+          range: (foldl' (invalidIds: id: invalidIds ++ (if badIdFunc id then [ id ] else [ ])) [ ] range)
         ) fullRanges
       );
       invalidIdNums = map (v: toIntBase10 v) invalidIds;

2025/day_2_perf.nix

@@ -0,0 +1,60 @@
+# nix eval -f ./day_2_perf.nix part2
+# nix eval -f ./day_2_perf.nix part2 --arg input 'builtins.readFile ./puzzle_cache/day_2_1'
+{
+  input ? (builtins.readFile ./puzzle_cache/day_2_0),
+}:
+with builtins;
+with import ./utils.nix;
+let
+  # part 2 any repeat num
+  isStrPatternRepeated =
+    str:
+    let
+      strLen = stringLength str;
+      maxSplit = strLen / 2; # Only check up to half length since it must repeat at least twice
+      splits = genList (i: i + 1) maxSplit;
+
+      checkSplit =
+        split:
+        if mod strLen split == 0 then
+          let
+            count = strLen / split;
+            firstElem = substring 0 split str;
+            checkElem =
+              index:
+              if index >= count then
+                true
+              else if substring (index * split) split str == firstElem then
+                checkElem (index + 1)
+              else
+                false;
+            allPartsEqual = checkElem 1;
+          in
+          allPartsEqual
+        else
+          false;
+    in
+    any checkSplit splits;
+
+  ranges = map (range: map (v: toIntBase10 v) (split "-" range)) (split "," input);
+
+  sumBadIdsInRange =
+    range:
+    let
+      from = elemAt range 0;
+      to = elemAt range 1;
+      ids = genList (i: from + i) (to - from + 1);
+      processId =
+        acc: id:
+        let
+          strId = toString id;
+        in
+        if isStrPatternRepeated strId then acc + id else acc;
+    in
+    (foldl' processId 0 ids);
+
+  sumAllBadIds = sum (map sumBadIdsInRange ranges);
+in
+{
+  part2 = sumAllBadIds;
+}

2025/utils.nix

@@ -5,7 +5,6 @@ rec {
   min = a: b: if a < b then a else b;
   max = a: b: if a > b then a else b;
   split = delim: input: filter (s: isString s && s != "") (builtins.split delim input);
-  reduce = foldl'; # foldl' (acc: elem: acc + elem) 0 [1 2 3]
   flatten = input: concatMap (x: if isList x then x else [ x ]) input;
   rangeInclusive =
     min: max:
@@ -16,7 +15,7 @@ rec {
         len = max - min + 1;
       in
       genList (i: min + i) len;
-  sum = input: reduce (sum: v: sum + v) 0 input;
+  sum = input: foldl' (sum: v: sum + v) 0 input;
   reverseList =
     list:
     if builtins.length list == 0 then
@@ -25,21 +24,5 @@ rec {
       # Recursively reverse the tail and append the head to the end
       (reverseList (builtins.tail list)) ++ [ (builtins.head list) ];
   splitStringByLength =
-    # @param s: The input string.
+    str: len: map (i: substring (i * len) (len) str) (genList (i: i) (stringLength str / len));
-    # @param len: The desired length of each part.
-    s: len:
-    let
-      # Recursive helper function
-      splitRec =
-        currentString: acc:
-        if stringLength currentString <= 0 then
-          reverseList acc
-        else
-          let
-            chunk = substring 0 len currentString;
-            remaining = substring len (stringLength currentString - len) currentString;
-          in
-          splitRec remaining ([ chunk ] ++ acc);
-    in
-    splitRec s [ ];
 }