1 files changed, 49 insertions, 0 deletions
diff --git a/2024/day_02.ml b/2024/day_02.ml
new file mode 100644
index 0000000..d05cb5c
--- /dev/null
+++ b/2024/day_02.ml
@@ -0,0 +1,49 @@
+let filename = "./day_02_input.txt"
+let try_read ic = try Some (input_line ic) with End_of_file -> None
+
+let is_values_safe a b direction =
+  match direction with
+  | "up" -> a < b && abs (a - b) < 4
+  | "down" -> a > b && abs (a - b) < 4
+  | _ -> false
+
+let direction a b = if a < b then "up" else "down"
+
+let is_line_safe list =
+  let a, b = (List.hd list, List.tl list |> List.hd) in
+  let direction = direction a b in
+  List.fold_left
+    (fun (acc, prev) x ->
+      if prev > -1 then (acc && is_values_safe prev x direction, x) else (acc, x))
+    (true, -1) list
+  |> fst
+
+let is_line_safe_part_2 list =
+  List.mapi
+    (fun i _ -> List.filteri (fun j _ -> j <> i) list |> is_line_safe)
+    list
+  |> List.exists (fun x -> x)
+
+let calculate_safe_score ic is_line_safe =
+  let rec calculate acc =
+    match try_read ic with
+    | Some line -> (
+        match
+          is_line_safe (String.split_on_char ' ' line |> List.map int_of_string)
+        with
+        | true -> calculate (acc + 1)
+        | false -> calculate acc)
+    | None ->
+        close_in ic;
+        acc
+  in
+  calculate 0
+
+let () =
+  let ic = open_in filename in
+  calculate_safe_score ic is_line_safe
+  |> Printf.sprintf "Safe %d" |> print_endline;
+
+  let ic = open_in filename in
+  calculate_safe_score ic is_line_safe_part_2
+  |> Printf.sprintf "Safe %d" |> print_endline