added comment & got rid of match%pcre

src/day7.ml

@@ -1,5 +1,6 @@
 open Containers
 
+(* could have simplified this a lot by getting rid of File *)
 type node =
   | File of
       { name : string
@@ -23,17 +24,13 @@ let get_dir_tree () =
            match node with
            | File _ -> failwith "current directory cannot be a file"
            | Dir dir ->
-             (match%pcre line with
-              | {|\$ ls|} -> node
-              | {|dir (?<name>.*)|} ->
+             (match String.split ~by:" " line with
+              | [ "$"; "ls" ] -> node
+              | [ "dir"; name ] ->
                 let new_dir = Dir { name; parent = Some (Dir dir); children = [] } in
                 dir.children <- new_dir :: dir.children;
                 node
-              | {|(?<size>\d+) (?<name>.*)|} ->
-                let new_file = File { name; size = int_of_string size } in
-                dir.children <- new_file :: dir.children;
-                node
-              | {|cd \.\.|} ->
+              | [ "$"; "cd"; ".." ] ->
                 (match dir.parent with
                  | Some parent -> parent
                  | _ ->
@@ -42,13 +39,17 @@ let get_dir_tree () =
                         "ERROR:%d: cant cd .. because node '%s' has no parent"
                         !line_num
                         dir.name)
-              | {|cd (?<name>.*)|} ->
+              | [ "$"; "cd"; name ] ->
                 dir.children
                 |> List.find (fun child ->
                   match child with
                   | Dir child_dir -> String.Infix.(name = child_dir.name)
                   | _ -> false)
-              | line -> failwith @@ Printf.sprintf "failed to parse line '%s'" line))
+              | [ size; name ] ->
+                let new_file = File { name; size = int_of_string size } in
+                dir.children <- new_file :: dir.children;
+                node
+              | _ -> failwith @@ Printf.sprintf "failed to parse line '%s'" line))
          tree
   in
   tree
@@ -87,8 +88,8 @@ let part2 () =
     ()
   in
   let used_space = get_node_size collect_dir_sizes tree in
-  let total_space = 70000000 in
-  let required_space = 30000000 in
+  let total_space = 70_000_000 in
+  let required_space = 30_000_000 in
   let free_space = total_space - used_space in
   match
     !dir_sizes