Improve day 3 char code math readability

ocaml/3.ml

@@ -4,9 +4,9 @@ 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
+  if code > Char.code 'Z'
+  then code - (Char.code 'a') + 1
+  else code - (Char.code 'A') + 27
 in
 
 let sum_of_priorities fn str =
@@ -48,7 +48,9 @@ let rec sum_badge_priorities sum lines =
 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 lines = String.split_on_char '\n' contents
+|> List.filter (fun l -> String.trim l <> "")
+in
 let sum1 = sum_rucksack_priorities lines in
 let sum2 = sum_badge_priorities 0 lines in
 Printf.printf "Part 1: %d\n" sum1;

ocaml/4.ml

@@ -0,0 +1,38 @@
+#use "lib/utils.ml" ;;
+
+let parse_range str =
+  let nums = String.split_on_char '-' str in
+  let start = int_of_string (List.nth nums 0) in
+  let rend = int_of_string (List.nth nums 1) in
+  (start, rend)
+in
+
+let is_full_overlap x y =
+  let ((x1, x2), (y1, y2)) = (x, y) in
+  (x1 >= y1 && x2 <= y2) || (y1 >= x1 && y2 <= x2)
+in
+
+let is_partial_overlap x y =
+  let ((x1, x2), (y1, y2)) = (x, y) in
+  not (x1 > y2 || x2 < y1)
+in
+
+let count_overlaps lines fn =
+  let check_overlap line =
+    let ranges = String.split_on_char ',' line in
+    let left = parse_range (List.nth ranges 0) in
+    let right = parse_range (List.nth ranges 1) in
+    if fn left right then 1 else 0
+  in
+  List.map check_overlap lines
+  |> List.fold_left (+) 0
+in
+
+let contents = read_file "inputs/4.txt" in
+let lines = String.split_on_char '\n' contents
+|> List.filter (fun l -> String.trim l <> "")
+in
+let nfull = count_overlaps lines is_full_overlap in
+let npartial = count_overlaps lines is_partial_overlap in
+Printf.printf "%d full overlaps\n" nfull;
+Printf.printf "%d partial overlaps\n" npartial