lantern fish???

AdventOfCode2024/bin/main.ml

@@ -13,7 +13,7 @@ let read_lines name =
 let () =
   print_endline "\nAdvent of Code 2024";
   let part1, part2 =
-    read_lines "./inputs/10.txt" |> AdventOfCode2024.Day_10.solve
+    read_lines "./inputs/11.txt" |> AdventOfCode2024.Day_11.solve
   in
   Printf.printf "Part 1: %s\nPart 2: %s\n" (string_of_int part1)
     (string_of_int part2)

AdventOfCode2024/lib/day_11.ml

@@ -0,0 +1,64 @@
+let line_to_numbers line =
+  String.split_on_char ' ' line |> List.map int_of_string
+
+module IntMap = Map.Make (Int)
+
+let num_of_digits num = (float_of_int num |> log10 |> int_of_float) + 1
+
+let split_stone num =
+  let digits = num_of_digits num in
+  let num_str = string_of_int num in
+  let first_half = String.sub num_str 0 (digits / 2) |> int_of_string in
+  let second_half =
+    String.sub num_str (digits / 2) (digits / 2) |> int_of_string
+  in
+  (first_half, second_half)
+
+let upsert k v map =
+  IntMap.update k
+    (fun existing ->
+      match existing with None -> Some v | Some i -> Some (i + v))
+    map
+
+let blink map =
+  IntMap.fold
+    (fun k v acc ->
+      if k == 0 then upsert 1 v acc
+      else if num_of_digits k mod 2 == 0 then
+        let first_stone, second_stone = split_stone k in
+        upsert first_stone v acc |> upsert second_stone v
+      else upsert (k * 2024) v acc)
+    map IntMap.empty
+
+let blink_times map times =
+  let rec loop acc times' =
+    match times' with 0 -> acc | t -> loop (blink acc) (t - 1)
+  in
+  loop map times
+
+let print_map map = IntMap.iter (Printf.printf "Key: %d, Value: %d\n") map
+
+let solve lines =
+  let line = List.nth lines 0 in
+  let nums = line_to_numbers line in
+
+  let filled_map =
+    List.fold_left
+      (fun acc i ->
+        IntMap.update i
+          (fun item ->
+            match item with None -> Some 1 | Some in_map -> Some (in_map + 1))
+          acc)
+      IntMap.empty nums
+  in
+
+  let part1 =
+    blink_times filled_map 25 |> IntMap.to_list
+    |> List.fold_left (fun acc (_, v) -> acc + v) 0
+  in
+
+  let part2 =
+    blink_times filled_map 75 |> IntMap.to_list
+    |> List.fold_left (fun acc (_, v) -> acc + v) 0
+  in
+  (part1, part2)