day 9

day9.ml

@@ -0,0 +1,78 @@
+(* 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 = f(g(x))
+let (>>) f g x = g(f(x))
+
+let rec take n (x :: xs) = (* take the first n elements *)
+  match n with
+  | 0 -> []
+  | n -> x :: (take (n-1) xs)
+
+let rec drop n l = (* drop the first n elemnts *)
+  match n with
+  | 0 -> l
+  | n -> drop (n-1) @@ List.tl l
+
+let sub_list start length = (* sub list from start *)
+  take length >> drop start
+
+let list_sum = List.fold_left (+) 0
+
+let list_max l = List.fold_left (fun acc x -> if x > acc then x else acc) (List.hd l) l
+let list_min l = List.fold_left (fun acc x -> if x < acc then x else acc) (List.hd l) l
+
+let range start len = (* makes a new list from start with length len *)
+  List.init len (fun x -> x + 0) |> List.map (fun x -> x + start)
+
+let flip f x y = f y x
+
+(* --- *)
+
+let has_adders l target = (* do any 2 elements of l add up to target *)
+  match List.find_opt (fun x ->
+      match List.find_opt (fun y -> x != y && x + y = target) l with
+      | Some _ -> true
+      | None -> false
+    ) l with
+  | Some _ -> true
+  | None -> false
+
+let rec first_without_adders pre lines =
+  let x :: xs = lines in (* match out the head and tail *)
+  let cur = List.nth lines pre in (* grab the first row after the preamble *)
+  let sub = take pre lines in (* grab the preamble sublist *)
+  if has_adders sub cur (* chechk for adders *)
+  then first_without_adders pre xs (* if it has adders, recurse with the tail of the original list *)
+  else cur (* no adders! return this one *)
+
+let rec all_sub_lists = function (* all combinations of sub-lists *)
+  | [] -> []
+  | xs ->
+      range 0 (List.length xs)
+      |> List.map (fun len' -> sub_list 0 len' xs)
+      |> flip List.append (all_sub_lists @@ List.tl xs)
+
+let () =
+  let lines = read_file "day9.txt" |> List.map int_of_string in
+
+  let first = lines |> first_without_adders 25 in
+  Printf.printf "first without 2 adders %i\n" first;
+
+  let all_subs = all_sub_lists lines in
+  let our_range = List.find (fun l -> list_sum l = first) all_subs in
+  let our_sum = (list_max our_range) + (list_min our_range) in
+  Printf.printf "sum %i\n" our_sum;