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86 lines
2.0 KiB
OCaml
86 lines
2.0 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 implode l = String.of_seq (List.to_seq l)
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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 flip f x y = f y x
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(* --- *)
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let rec find_idx x = function (* find index of x *)
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| [] -> raise (Failure "Not Found")
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| h :: t -> if x = h then 0 else 1 + find_idx x t
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let rec last = function
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| [] -> raise (Failure "Empty List")
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| x :: [] -> x
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| x :: xs -> last xs
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let hash = Hashtbl.create 1000
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let rec go idx last num =
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(* Printf.printf "\nidx: %i. last num: %i\n" idx num; *)
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if idx = last - 1
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then num
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else
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let next =
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try
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let idx' = Hashtbl.find hash num in
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let new_num = idx - idx' in
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new_num
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with Not_found _ -> 0
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in
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let _ = Hashtbl.replace hash num idx in
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go (idx+1) last next
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let () =
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let nums = read_file "day15.txt"
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|> flip List.nth 0 (* grab the first line *)
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|> String.split_on_char ','
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|> List.map int_of_string
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in
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List.iter (Printf.printf "%i ") nums;
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print_newline ();
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(* pluck out the last number to start things off *)
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let rev = List.rev nums in
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let x :: xs = rev in
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let nums' = List.rev xs in
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let starting_idx = List.length xs in
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(* Add the initial list to our hash *)
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List.iteri (fun i x -> Hashtbl.add hash x i;) nums';
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let final = go starting_idx 2020 x in
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Printf.printf "after 2020: %i\n" final;
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Hashtbl.clear hash;
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List.iteri (fun i x -> Hashtbl.add hash x i;) nums';
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let final' = go starting_idx 30000000 x in
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Printf.printf "after 30000000: %i\n" final';
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