day 7

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/06.txt" |> AdventOfCode2024.Day_06.solve
+    read_lines "./inputs/07.txt" |> AdventOfCode2024.Day_07.solve
   in
   Printf.printf "Part 1: %s\nPart 2: %s\n" (string_of_int part1)
     (string_of_int part2)

AdventOfCode2024/lib/day_07.ml

@@ -0,0 +1,67 @@
+type equation = { equals : int; numbers : int list }
+
+let rec print_list l =
+  match l with
+  | [] -> print_endline ""
+  | head :: tail ->
+      print_int head;
+      print_string ",";
+      print_list tail
+
+let equation_from_line line =
+  let first_num = Scanf.sscanf line "%d:" (fun n1 -> n1) in
+  let rest_of_numbers =
+    List.nth (String.split_on_char ':' line) 1
+    |> String.trim |> String.split_on_char ' '
+  in
+  let numbers = List.map int_of_string rest_of_numbers in
+  { equals = first_num; numbers }
+
+let attempt_solve { equals; numbers } =
+  (* [1, 2] *)
+  let rec loop numbers =
+    match numbers with
+    | head :: [] -> [ head ]
+    | head :: tail ->
+        let plus = List.map (fun i -> i + head) (loop tail) in
+        let times = List.map (fun i -> i * head) (loop tail) in
+        plus @ times
+    | _ -> raise (Invalid_argument "")
+  in
+  let possibilities = loop (List.rev numbers) in
+  if List.exists (fun i -> i == equals) possibilities then equals else 0
+
+let attempt_solve_part2 { equals; numbers } =
+  (* [1, 2] *)
+  let rec loop numbers =
+    match numbers with
+    | head :: [] -> [ head ]
+    | head :: tail ->
+        let plus = List.map (fun i -> i + head) (loop tail) in
+        let times = List.map (fun i -> i * head) (loop tail) in
+        let concat =
+          List.map
+            (fun i ->
+              let i_string = string_of_int i in
+              let head_string = string_of_int head in
+              int_of_string (i_string ^ head_string))
+            (loop tail)
+        in
+        plus @ times @ concat
+    | _ -> raise (Invalid_argument "")
+  in
+  let possibilities = loop (List.rev numbers) in
+  if List.exists (fun i -> i == equals) possibilities then equals else 0
+
+let solve lines =
+  let part1 =
+    List.fold_left
+      (fun acc line -> acc + (equation_from_line line |> attempt_solve))
+      0 lines
+  in
+  let part2 =
+    List.fold_left
+      (fun acc line -> acc + (equation_from_line line |> attempt_solve_part2))
+      0 lines
+  in
+  (part1, part2)