Day 3

ocaml/3.ml

@@ -0,0 +1,55 @@
+#use "lib/file_utils.ml" ;;
+
+let priority_of_item c =
+  (* ASCII lower case is 97-122, upper case is 65-90 *)
+  (* Lower case start at 1, upper case at 27 *)
+  let code = Char.code c in
+  if code > 90
+  then code - 96
+  else code - 65 + 27
+in
+
+let sum_of_priorities fn str =
+  let chars = List.sort_uniq compare (list_of_chars str) in
+  List.fold_left fn 0 chars
+in
+
+let sum_rucksack_priorities lines =
+  let rucksack_priority str =
+    let len2 = (String.length str)/2 in
+    let comp1 = String.sub str 0 len2 in
+    let comp2 = String.sub str len2 len2 in
+    let char_priority agg c =
+      if String.contains comp2 c
+      then (agg + priority_of_item c)
+      else agg
+    in
+    sum_of_priorities char_priority comp1
+  in
+  List.fold_left (+) 0 (List.map rucksack_priority lines)
+in
+
+let rec sum_badge_priorities sum lines =
+  let common_badge_priority str1 str2 str3 =
+    let char_priority agg c =
+      if String.contains str2 c && String.contains str3 c
+      then (agg + priority_of_item c)
+      else agg
+    in
+    sum_of_priorities char_priority str1
+  in
+  match lines with
+    | [] -> sum
+    | hd1 :: tl1 -> match tl1 with
+      | [] -> failwith "number of rows must be divisible by 3"
+      | hd2 :: tl2 -> match tl2 with
+        | [] -> failwith "number of rows must be divisible by 3"
+        | hd3 :: tl3 -> sum_badge_priorities (sum + common_badge_priority hd1 hd2 hd3) tl3
+in
+
+let contents = read_file "inputs/3.txt" in
+let lines = List.filter (fun l -> String.trim l <> "") (String.split_on_char '\n' contents) in
+let sum1 = sum_rucksack_priorities lines in
+let sum2 = sum_badge_priorities 0 lines in
+Printf.printf "Part 1: %d\n" sum1;
+Printf.printf "Part 2: %d\n" sum2

ocaml/lib/file_utils.ml

@@ -4,3 +4,5 @@ let read_file filename =
   close_in ch;
   s
   ;;
+
+let list_of_chars str = List.init (String.length str) (String.get str)