day 2

day2.ml

@@ -0,0 +1,45 @@
+let read_file_rev name =
+    let ic = open_in name in
+    let try_read () =
+        try Some (input_line ic)
+        with End_of_file -> None in
+    let rec loop acc =
+        match try_read () with
+        | Some s -> loop (s::acc)
+        | None -> close_in ic; acc in
+    loop []
+
+
+let count_good_passwords f l =
+    let is_conforming f entry =
+        let [term; pass] = String.split_on_char ':' entry in
+        let [rep; letter] = String.split_on_char ' ' term in
+        let [minr; maxr] = List.map int_of_string (String.split_on_char '-' rep) in
+        f pass minr maxr letter.[0] in
+    List.map (is_conforming f) l
+        |> List.map (fun b -> if b then 1 else 0)
+        |> List.fold_left (+) 0
+
+
+let part1_f pass minr maxr letter =
+    let count = List.length (String.split_on_char letter pass) - 1 in
+    minr <= count && count <= maxr
+
+let part2_f pass first second letter =
+    let position_matches pass pos letter =
+        match String.get pass pos with
+        | c -> c = letter
+        | _ -> false in
+    (position_matches pass first letter) <> (position_matches pass second letter)
+
+
+let do_count filename = function
+    | 1 -> read_file_rev filename |> count_good_passwords part1_f
+    | 2 -> read_file_rev filename |> count_good_passwords part2_f
+
+
+let () =
+    print_endline (string_of_int (do_count "day2.input" 1))
+
+let () =
+    print_endline (string_of_int (do_count "day2.input" 2))