day 2 part 2

2025/day_2.nix

@@ -8,12 +8,7 @@
 with builtins;
 with import ./utils.nix;
 let
-  # reversedChars =
-  #   str:
-  #   let
-  #     len = length str;
-  #   in
-  #   builtins.genList (i: builtins.elemAt str (len - 1 - i)) len;
+  # part 1 simple repeat middle of word
   isStrPatternSplit =
     str:
     let
@@ -25,27 +20,46 @@ let
           half = strLen / 2;
           firstHalf = substring 0 half str;
           secondHalf = substring half strLen str;
-          # secondReversed = reversedChars secondHalf;
         in
         firstHalf == secondHalf
       else
         false
     );
+  # part 2 any repeat num
+  isStrPatternRepeated =
+    str:
+    let
+      strLen = stringLength str;
+      splits = reverseList (genList (i: i + 1) strLen);
+    in
+    any (
+      split:
+      if split < strLen && mod strLen split == 0 then
+        let
+          parts = splitStringByLength str split;
+        in
+        all (e: e == elemAt parts 0) parts
+      else
+        false
+    ) splits;
 
   ranges = map (range: map (v: toIntBase10 v) (split "-" range)) (split "," input);
   fullRanges = map (itr: map (v: toString v) (rangeInclusive (elemAt itr 0) (elemAt itr 1))) ranges;
-  invalidIds = flatten (
-    map (
-      range:
-      (reduce (
-        invalidIds: id: invalidIds ++ (if isStrPatternSplit id then [ id ] else [ ])
-      ) [ ] range)
-    ) fullRanges
-  );
-  invalidIdNums = map (v: toIntBase10 v) invalidIds;
-  invalidIdSum = sum invalidIdNums;
+
+  getSumOfBadIdsGivenBadIdFunc =
+    badIdFunc:
+    let
+      invalidIds = flatten (
+        map (
+          range: (reduce (invalidIds: id: invalidIds ++ (if badIdFunc id then [ id ] else [ ])) [ ] range)
+        ) fullRanges
+      );
+      invalidIdNums = map (v: toIntBase10 v) invalidIds;
+      invalidIdSum = sum invalidIdNums;
+    in
+    invalidIdSum;
 in
 {
-  part1 = invalidIdSum;
-  part2 = 0;
+  part1 = getSumOfBadIdsGivenBadIdFunc isStrPatternSplit;
+  part2 = getSumOfBadIdsGivenBadIdFunc isStrPatternRepeated;
 }

2025/utils.nix

@@ -4,7 +4,7 @@ rec {
   mod = a: b: a - b * (floor (a / b));
   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 != "") (split delim input);
+  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 =
@@ -17,4 +17,29 @@ rec {
       in
       genList (i: min + i) len;
   sum = input: reduce (sum: v: sum + v) 0 input;
+  reverseList =
+    list:
+    if builtins.length list == 0 then
+      [ ]
+    else
+      # Recursively reverse the tail and append the head to the end
+      (reverseList(builtins.tail list)) ++ [ (builtins.head list) ];
+  splitStringByLength =
+    # @param s: The input string.
+    # @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 [ ];
 }