2025: day3: ocaml

AdventOfCode2025/day3/bin/dune

@@ -0,0 +1,3 @@
+(executable
+ (public_name day3)
+ (name main))

AdventOfCode2025/day3/bin/main.ml

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+let get_highest_number_and_index l =
+    let (t, _) = List.fold_left (
+        fun ((highest, highest_index), index) i -> 
+            if i > highest then 
+                ((i, index), index + 1) 
+        else 
+            ((highest, highest_index), index + 1)
+    ) ((0, 0), 0) (List.rev l) in
+    t
+
+let rec first_n k xs = match xs with
+| [] -> failwith "firstk"
+| x::xs -> if k=1 then [x] else x::first_n (k-1) xs
+
+let slice_at_index l index =
+    let rec loop (i, acc) =
+        match acc with
+        | [] -> failwith "too far"
+        | _ :: tail -> if i == index then tail else loop (i + 1, tail)
+    in
+    loop (0, List.rev l)
+
+let highest_n n l =
+    let rec loop acc n l =
+        match n with
+        | 0 -> acc
+        | n -> 
+            let list_first_n_items = first_n (List.length l - n + 1) (List.rev l) |> List.rev  in
+            let (highest, highest_index) = get_highest_number_and_index list_first_n_items in
+            let remaining_list = slice_at_index l highest_index in
+            loop (highest :: acc) (n - 1) (List.rev remaining_list)
+        in
+    loop [] n l
+            
+let string_to_int_list l =
+    l 
+    |> String.to_seq  
+    |> List.of_seq 
+    |> List.fold_left (fun acc i -> ((int_of_char i) - (int_of_char '0')) :: acc) []
+
+let num_from_int_list l =
+    let rec loop acc index l =
+        match l with
+        | [] -> acc
+        | head :: tail -> loop (acc + index * head) (index * 10) tail
+    in
+    loop 0 1 l
+            
+
+
+let solve lines =
+    let nums_part1 = List.fold_left (
+        fun acc line -> (line |> string_to_int_list |> (highest_n 2)) :: acc
+    ) [] lines in
+
+    let part1 = List.fold_left (+) 0 (List.map num_from_int_list nums_part1) in
+
+    let nums_part2 = List.fold_left (
+        fun acc line -> (line |> string_to_int_list |> (highest_n 12)) :: acc
+    ) [] lines in
+
+    let part2 = List.fold_left (+) 0 (List.map num_from_int_list nums_part2) in
+
+    (part1, part2)
+
+let read_lines 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;
+        List.rev acc
+  in
+  loop []
+
+let () =
+print_endline "Day 3";
+  let part1, part2 =
+    read_lines "./input.txt" |> solve
+  in
+  Printf.printf "Part 1: %s\nPart 2: %s\n" (string_of_int part1)
+    (string_of_int part2)
+
+