day 14. still not done with 13..

day14.ml

@@ -0,0 +1,119 @@
+(* 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 explode s = (* convert a string to a list of chars *)
+  let rec exp i l =
+   if i < 0 then l else exp (i - 1) (s.[i] :: l) in
+  exp (String.length s - 1) [];;
+
+let implode l = String.of_seq (List.to_seq l)
+
+let (<<) f g x = f(g(x))
+let (>>) f g x = g(f(x))
+
+let abs x = if x < 0 then -x else x
+
+(* --- *)
+
+type instruction = Mask of string | Mem of int * int (* Mem (addr, value) *)
+
+let parse_instruction : string -> instruction =
+  String.split_on_char '='
+  >> List.map String.trim
+  >> fun [left; right] ->
+    if left = "mask"
+    then Mask right
+    else
+      let len = String.length left in
+      let addr = String.sub left 4 (len - 5) in
+      Mem (int_of_string addr, int_of_string right)
+
+let rec pow a = function
+  | 0 -> 1
+  | 1 -> a
+  | n ->
+      let b = pow a (n / 2) in
+      b * b * (if n mod 2 = 0 then 1 else a)
+
+let bin2dec =
+  List.rev
+  >> List.mapi (fun i d -> if d = 1 then pow 2 i else 0)
+  >> List.fold_left (+) 0
+
+let int_of_char = String.make 1 >> int_of_string
+
+let run_mask mask num = (* 'and' the 0s and 'or' the 1s *)
+  let l = explode mask in
+  let ones = List.map (fun c -> if c = '1' then '1' else '0') l (* copy the mask but just the ones *)
+    |> List.map int_of_char |> bin2dec in (* convert from char list to int list to decimal int *)
+  let zeros = List.map (fun c -> if c = '0' then '1' else '0') l (* same for zeros but make all the zeros 1s *)
+    |> List.map int_of_char |> bin2dec in
+  (num lor ones) - (num land zeros) (* subtract! *)
+
+let change_bit number position new_value =
+  let mask = 1 lsl position in
+  (number land (lnot mask)) lor ((new_value lsl position) land mask)
+
+let rec find_addrs mask addr = (* return a list of all addresses after applying mask with floaty bit *)
+  let mask' = List.rev @@ explode mask in
+  Printf.printf "\nnew mask! %s\n" mask;
+
+  let rec go addr' idx =
+    if idx = List.length mask'
+    then [addr']
+    else
+      let cur = List.nth mask' idx in
+
+      if cur = '0'
+      then go addr' (idx + 1)
+      else
+        if cur = '1'
+        then go (change_bit addr' idx 1) (idx + 1)
+        else (* X *)
+          let addr0 = (change_bit addr' idx 0) in
+          let addr1 = (change_bit addr' idx 1) in
+          List.concat [go addr0 (idx + 1); go addr1 (idx + 1)]
+  in go addr 0
+
+let hash = Hashtbl.create 1000
+let hash' = Hashtbl.create 1000
+
+let rec walk mask = function
+  | [] -> ()
+  | x :: xs ->
+      match x with
+      | Mask m -> walk m xs (* update the mask and recurse *)
+      | Mem (addr, value) ->
+          (* problem 1 *)
+          run_mask mask value
+          |> Hashtbl.replace hash addr;
+
+          (* problem 2 *)
+          find_addrs mask addr
+          |> List.iter (fun addr' -> Hashtbl.replace hash' addr' value;);
+
+          walk mask xs (* recurse *)
+
+let () =
+  let lines = read_file "day14.txt" |> List.map parse_instruction in
+
+  walk "" lines;
+
+  let sum = Hashtbl.fold (fun k v acc -> acc + v) hash 0 in
+  Printf.printf "sum: %i\n" sum;
+
+  let sum' = Hashtbl.fold (fun k v acc -> acc + v) hash' 0 in
+  Printf.printf "sum': %i\n" sum';