d22

22/main.ml

@@ -0,0 +1,72 @@
+open Printf;;
+
+let rec list_of_lines in_file =
+  try
+    let line = input_line in_file in
+    line :: list_of_lines(in_file)
+  with End_of_file ->
+    close_in in_file;
+    []
+
+let mix_and_prune x y =
+  Int.logand (Int.logxor x y) 0xffffff
+
+let next_in_sequence x =
+  let x1 = mix_and_prune x (Int.shift_left x 6) in
+  let x2 = mix_and_prune x1 (Int.shift_right x1 5) in
+  mix_and_prune x2 (Int.shift_left x2 11)
+
+let rec skip_sequence times x =
+  if times = 0 then
+    x
+  else skip_sequence (times - 1) (next_in_sequence x)
+
+let make_indexing_array () =
+  Array.make 130321 0
+
+let get_sequence_index (x1, x2, x3, x4) =
+  (x1 + 9) + (x2 + 9) * 19 + (x3 + 9) * 361 + (x4 + 9) * 6859
+
+let mod10_diff x1 x2 =
+  (x1 mod 10) - (x2 mod 10)
+
+module IntSet = Set.Make(Int)
+
+let rec index_monkey_inner indexing_array already_occured_set current sequence seq_length =
+  if seq_length > 0 then
+    let index = get_sequence_index sequence in
+    let new_set = if IntSet.find_opt index already_occured_set |> Option.is_none then begin
+      indexing_array.(index) <- indexing_array.(index) + (current mod 10);
+      IntSet.add index already_occured_set
+    end else
+      already_occured_set in
+    let new_value = next_in_sequence current in
+    let diff = mod10_diff new_value current in
+    let (d1, d2, d3, _) = sequence in
+    index_monkey_inner indexing_array new_set new_value (diff, d1, d2, d3) (seq_length - 1)
+
+let index_monkey indexing_array seq_length seed =
+  let s4 = next_in_sequence seed in
+  let s3 = next_in_sequence s4 in
+  let s2 = next_in_sequence s3 in
+  let s1 = next_in_sequence s2 in
+  let d1 = mod10_diff s1 s2 in
+  let d2 = mod10_diff s2 s3 in
+  let d3 = mod10_diff s3 s4 in
+  let d4 = mod10_diff s1 seed in
+  index_monkey_inner indexing_array IntSet.empty s1 (d1, d2, d3, d4) (seq_length - 4)
+
+let decode_index index = 
+  (index mod 19 - 9, (index / 19) mod 19 - 9, (index / 361) mod 19 - 9, (index / 6859) mod 19 - 9)
+
+let () =
+  let () = Printexc.record_backtrace true in
+  let f = open_in "input.txt" in
+  let monkey_seeds = list_of_lines f |> List.map int_of_string in
+  let result = monkey_seeds
+  |> List.map (skip_sequence 2000)
+  |> List.fold_left Int.add 0 in
+  let indexing_array = make_indexing_array () in
+  List.iter (index_monkey indexing_array 2000) monkey_seeds;
+  let result2 = Array.fold_left Int.max 0 indexing_array in
+  printf "%d\n%d\n" result result2