1 files changed, 60 insertions, 0 deletions
diff --git a/2024/day_03.ml b/2024/day_03.ml
new file mode 100644
index 0000000..acd1391
--- /dev/null
+++ b/2024/day_03.ml
@@ -0,0 +1,60 @@
+let filename = "./day_03_input.txt"
+let try_read ic = try Some (input_line ic) with End_of_file -> None
+
+let read_file ic =
+  let rec read acc =
+    match try_read ic with
+    | Some line -> read (line :: acc)
+    | None ->
+        close_in ic;
+        acc
+  in
+  read [] |> List.rev |> String.concat ""
+
+let regex = Str.regexp "mul(\\([0-9]+\\),\\([0-9]+\\))"
+let regex_mul_part_2 = Str.regexp "mul(\\([0-9]+\\),\\([0-9]+\\))\\|don't()"
+let regex_do_part_2 = Str.regexp "do()"
+
+let calculate_total str =
+  let rec calculate str acc =
+    try
+      let _ = Str.search_forward regex str 0 in
+      let a = Str.matched_group 1 str |> int_of_string in
+      let b = Str.matched_group 2 str |> int_of_string in
+
+      let result = a * b in
+      let new_str = Str.replace_first regex (string_of_int result) str in
+      calculate new_str (acc + result)
+    with Not_found -> acc
+  in
+  calculate str 0
+
+let calculate_total_part_2 str =
+  let rec calculate str regexp acc =
+    try
+      let _ = Str.search_forward regexp str 0 in
+      let cmd = Str.matched_group 0 str in
+      let new_str =
+        String.sub str (Str.match_end ()) (String.length str - Str.match_end ())
+      in
+      match cmd with
+      | "do()" -> calculate new_str regex_mul_part_2 acc
+      | "don't()" -> calculate new_str regex_do_part_2 acc
+      | cmd when String.starts_with ~prefix:"mul" cmd ->
+          let a = Str.matched_group 1 str |> int_of_string in
+          let b = Str.matched_group 2 str |> int_of_string in
+          let result = a * b in
+          calculate new_str regexp (acc + result)
+      | _ -> acc
+    with Not_found -> acc
+  in
+  calculate str regex_mul_part_2 0
+
+let () =
+  let ic = open_in filename in
+  read_file ic |> calculate_total |> Printf.sprintf "Sum %d" |> print_endline;
+
+  let ic = open_in filename in
+  read_file ic |> calculate_total_part_2
+  |> Printf.sprintf "Part 2 Sum %d"
+  |> print_endline