3 files changed, 111 insertions(+), 0 deletions(-)

A 9/lex.mll
A 9/t1.ml
A 9/t2.ml

@@ 0,0 1,11 @@
+{
+type token =
+	| Line of char * int
+	| Eof
+
+let i = int_of_string
+}
+
+rule token = parse
+  | (['A'-'Z'] as c) ' ' (['0'-'9']+ as s) '\n' { Line (c, i s) }
+	| eof { Eof }

@@ 0,0 1,49 @@
+let rec f lexbuf =
+	match Lex.token lexbuf with
+	| Eof -> []
+	| Line (c, i) ->
+			let dir =
+				match c with
+				| 'L' -> (-1, 0)
+				| 'R' -> (1, 0)
+				| 'U' -> (0, 1)
+				| 'D' -> (0, -1)
+				| _ -> failwith "wut"
+			in
+			(dir, i) :: f lexbuf
+
+module PairSet = Set.Make(
+	struct
+		type t = int * int
+		let compare = compare
+	end
+)
+
+let move' (x, y) (dx, dy) = x + dx, y + dy
+
+let move_follow ((x, y) as tail) (x', y') =
+	let d =
+		match x'- x, y' - y with
+		| dx, dy when abs dx = 2 -> dx / 2, dy
+		| dx, dy when abs dy = 2 -> dx, dy / 2
+		| _ -> 0, 0
+	in
+	move' tail d
+
+let move_tail set tail head =
+	let newtail = move_follow tail head in
+	(PairSet.add newtail set, newtail, head)
+
+let rec move ((set, tail, head) as state) (d, n) =
+	match n with
+	| 0 -> state
+	| n -> move (move_tail set tail (move' head d)) (d, n - 1)
+
+let () =
+	stdin
+		|> Lexing.from_channel
+		|> f
+		|> List.fold_left move (PairSet.singleton (0, 0), (0, 0), (0, 0))
+		|> fun (x, _, _) -> x
+		|> PairSet.cardinal
+		|> Printf.printf "%d\n"

@@ 0,0 1,51 @@
+let rec f lexbuf =
+	match Lex.token lexbuf with
+	| Eof -> []
+	| Line (c, i) ->
+			let dir =
+				match c with
+				| 'L' -> (-1, 0)
+				| 'R' -> (1, 0)
+				| 'U' -> (0, 1)
+				| 'D' -> (0, -1)
+				| _ -> failwith "wut"
+			in
+			(dir, i) :: f lexbuf
+
+module PairSet = Set.Make(
+	struct
+		type t = int * int
+		let compare = compare
+	end
+)
+
+let move' (x, y) (dx, dy) = x + dx, y + dy
+
+let move_follow (x', y') ((x, y) as tail) =
+	let d =
+		match x' - x, y' - y with
+		| dx, dy when abs dx = 2 -> dx / 2, dy
+		| dx, dy when abs dy = 2 -> dx, dy / 2
+		| _ -> 0, 0
+	in
+	let tail = move' tail d in
+	tail, tail
+
+let move_tail set tail head =
+	let last, tail = List.fold_left_map move_follow head tail in
+	(PairSet.add last set, tail, head)
+
+let rec move ((set, tail, head) as state) (d, n) =
+	match n with
+	| 0 -> state
+	| n -> move (move_tail set tail (move' head d)) (d, n - 1)
+
+let () =
+	let init = List.init 8 (fun _ -> (0, 0)) in
+	stdin
+		|> Lexing.from_channel
+		|> f
+		|> List.fold_left move (PairSet.singleton (0, 0), init, (0, 0))
+		|> fun (x, _, _) -> x
+		|> PairSet.cardinal
+		|> Printf.printf "%d\n"