Day 4

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