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91 lines
2.3 KiB
OCaml
91 lines
2.3 KiB
OCaml
(* Common util. Should probably put this in a module or something.. *)
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let get_one_line file =
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try Some (input_line file) with
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End_of_file -> None
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let get_lines file =
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let rec input lines =
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match get_one_line file with
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Some line -> input (line :: lines)
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| None -> List.rev lines
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in input []
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let read_file file =
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let channel = open_in(file) in
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get_lines channel
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let explode s = (* convert a string to a list of chars *)
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let rec exp i l =
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if i < 0 then l else exp (i - 1) (s.[i] :: l) in
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exp (String.length s - 1) []
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let (<<) f g x = f(g(x))
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let (>>) f g x = g(f(x))
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let rec take n l = (* take the first n elements *)
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match n with
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| 0 -> []
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| n ->
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match l with
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| [] -> []
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| x :: xs -> x :: (take (n-1) xs)
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let rec drop n l = (* drop the first n elemnts *)
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match n with
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| 0 -> l
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| n -> drop (n-1) @@ List.tl l
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let c2i = String.make 1 >> int_of_string
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(* --- *)
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type exp = Add of exp * exp | Mul of exp * exp | Num of int
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let rec string_of_exp = function
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| Num x -> string_of_int x
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| Mul (a, b) -> Printf.sprintf "(%s * %s)" (string_of_exp a) (string_of_exp b)
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| Add (a, b) -> Printf.sprintf "(%s + %s)" (string_of_exp a) (string_of_exp b)
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let print_exp = print_string << string_of_exp
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let print_exps = List.iter print_exp
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let rec find_matching_paren count (x::xs) =
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match x with
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| '(' -> if count = 0 then 0 else 1 + find_matching_paren (count-1) xs
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| ')' -> 1 + find_matching_paren (count+1) xs
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| n -> 1 + find_matching_paren count xs
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let read_exp line =
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let line' = line
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|> explode
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|> List.filter (fun x -> x != ' ')
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|> List.rev
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in
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let rec go stack = function
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| [] -> List.hd stack
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| '+' :: xs -> Add (List.hd stack, (go (List.tl stack) xs))
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| '*' :: xs -> Mul (List.hd stack, (go (List.tl stack) xs))
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| ')' :: xs ->
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let matching = 1 + find_matching_paren 0 xs in
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let sub = take matching xs in
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let rest = drop matching xs in
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go ((go [] sub)::stack) rest
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| '(' :: xs -> List.hd stack
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| num :: xs -> go ((Num (c2i num)) :: stack) xs
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in
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go [] line'
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let rec eval = function
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| Num a -> a
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| Add (a, b) -> (eval a) + (eval b)
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| Mul (a, b) -> (eval a) * (eval b)
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let () =
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let exps = read_file "day18.txt" |> List.map read_exp in
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let values = List.map eval exps in
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let sum = List.fold_left (+) 0 values in
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print_int sum;
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