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