Advent of Code 2020 https://adventofcode.com/
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(* Common util. Should probably put this in a module or something.. *)
let get_one_line file =
try Some (input_line file) with
End_of_file -> None
let get_lines file =
let rec input lines =
match get_one_line file with
Some line -> input (line :: lines)
| None -> List.rev lines
in input []
let read_file file =
let channel = open_in(file) in
get_lines channel
let (>>) f g x = g(f(x))
let list_max l = List.fold_left (fun acc x -> if x > acc then x else acc) (List.hd l) l
let map_tuple f (a, b) = (f a, f b)
let memo_rec f =
let h = Hashtbl.create 1000 in
let rec g x =
try Hashtbl.find h x
with Not_found ->
let y = f g x in
Hashtbl.add h x y;
y
in g
(* --- *)
let rec collect_diffs = function
| x :: y :: [] -> [y - x] (* 2 elemnts left *)
| x :: y :: z -> y - x :: collect_diffs (y :: z)
let count_steps = (* returns a tuple of counts of 1's and 3's *)
List.partition (Int.equal 1)
>> map_tuple List.length
let count_valid self = function
| x :: y :: [] -> if y - x < 4 then 1 else 0
| x :: y :: rest ->
if y - x > 3
then 0
else self (x :: rest) + self (y :: rest)
let count_valid_memo = memo_rec count_valid
let () =
let lines = read_file "day10.txt"
|> List.map int_of_string
in
let adapter_jolts = 3 + list_max lines in
let sorted = lines
|> List.cons adapter_jolts (* add our adapter *)
|> List.cons 0 (* add the outlet *)
|> List.sort (fun x y -> if x > y then 1 else if x < y then -1 else 0)
in
sorted
|> collect_diffs
|> count_steps
|> fun (x, y) -> x * y
|> Printf.printf "prod: %i\n";
sorted
|> count_valid_memo
|> Printf.printf "\nsum: %i\n"