Day 6!

day6.ml

@@ -0,0 +1,70 @@
+
+(* 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 cl = String.concat "" (List.map (String.make 1) cl)
+
+let (<<) f g x = f(g(x)) (* how is 'compose' not in the standard library.. *)
+let (>>) f g x = g(f(x))
+
+let string_of_char = String.make 1
+
+(* --- *)
+
+let fix_lines glue_char lines = (* puts each group on 1 line *)
+  let glue s = if String.equal s "" then "\n" else glue_char in (* which char to concat the lines *)
+  let fix_line acc cur = acc ^ (glue cur) ^ cur in
+  List.fold_left fix_line "" lines
+
+let dedup =
+  explode >> (* string -> char list *)
+  List.fold_left (fun acc x -> if String.contains acc x then acc else acc ^ (string_of_char x)) ""
+
+let intersection group = (* find the chars common to all individuals in a group *)
+  List.fold_left (^) "" group (* *all* of the chars among individuals *)
+    |> dedup (* deduped *)
+    |> explode (* string to char list *)
+    |> List.filter (fun c -> List.for_all (fun g -> String.contains g c) group) (* check each char among each individual for membership *)
+    |> implode (* turn it back into a string *)
+
+let () =
+  let file = read_file "day6.txt" in
+
+  let any_sum = file
+    |> fix_lines "" (* put each group on one line *)
+    |> String.split_on_char '\n' (* convert to list *)
+    |> List.map dedup (* remove dups *)
+    |> List.map String.length (* make list of lengths *)
+    |> List.fold_left (+) 0 (* sum list *)
+  in
+
+  let all_sum = file
+    |> fix_lines " " (* keep spaces between individuals *)
+    |> String.split_on_char '\n'
+    |> List.map String.trim
+    |> List.map (String.split_on_char ' ') (* each line now is a list of groups *)
+    |> List.map intersection (* list of strings with intersecting chars *)
+    |> List.map String.length (* list of lengths *)
+    |> List.fold_left (+) 0 (* sum list *)
+  in
+
+  Printf.printf "any_sum %i\n" any_sum;
+  Printf.printf "all_sum %i\n" all_sum;