Day 1

lib/problems/problem_2023_01.ml

@@ -0,0 +1,78 @@
+let year = 2023
+let day = 1
+
+module Part_1 = struct
+  let run (input : string) : (string, string) result =
+    let string_to_digits s =
+      String.to_seq s |> Seq.map Char.escaped |> Seq.map int_of_string_opt
+      |> Seq.flat_map Option.to_seq |> Seq.map Int.to_string |> List.of_seq
+    in
+    let rec concat_digits = function
+      | [] -> 0
+      | [ x ] -> int_of_string (x ^ x)
+      | [ first; last ] -> int_of_string (first ^ last)
+      | first :: _ :: xs -> concat_digits (first :: xs)
+    in
+    let result =
+      String.split_on_char '\n' input
+      |> List.map string_to_digits |> List.map concat_digits
+      |> List.fold_left ( + ) 0 |> Int.to_string
+    in
+    Ok result
+end
+
+module Part_2 = struct
+  let run (input : string) : (string, string) result =
+    let word_to_digit_list =
+      [
+        ("one", "1");
+        ("two", "2");
+        ("three", "3");
+        ("four", "4");
+        ("five", "5");
+        ("six", "6");
+        ("seven", "7");
+        ("eight", "8");
+        ("nine", "9");
+        ("1", "1");
+        ("2", "2");
+        ("3", "3");
+        ("4", "4");
+        ("5", "5");
+        ("6", "6");
+        ("7", "7");
+        ("8", "8");
+        ("9", "9");
+      ]
+    in
+    let rec find_first_digit string =
+      match
+        List.find_opt
+          (fun (word, _) -> String.starts_with ~prefix:word string)
+          word_to_digit_list
+      with
+      | Some (_, digit) -> digit
+      | None ->
+          find_first_digit (String.sub string 1 (String.length string - 1))
+    in
+    let rec find_last_digit string =
+      match
+        List.find_opt
+          (fun (word, _) -> String.ends_with ~suffix:word string)
+          word_to_digit_list
+      with
+      | Some (_, digit) -> digit
+      | None -> find_last_digit (String.sub string 0 (String.length string - 1))
+    in
+    let concat_digits s =
+      let first = find_first_digit s in
+      let last = find_last_digit s in
+      int_of_string (first ^ last)
+    in
+    let result =
+      input |> String.split_on_char '\n'
+      |> List.filter (fun s -> String.length s > 0)
+      |> List.map concat_digits |> List.fold_left ( + ) 0 |> Int.to_string
+    in
+    Ok result
+end