refactor(2025d4): refactor part 2 to prep for recursion

1 files changed, 30 insertions, 25 deletions

diff --git a/2025/ocaml/lib/application/d04p02.ml b/2025/ocaml/lib/application/d04p02.ml
index 7c69de4..c53811a 100644
--- a/2025/ocaml/lib/application/d04p02.ml
+++ b/2025/ocaml/lib/application/d04p02.ml
@@ -2,31 +2,29 @@ open Domain
 
 let err_empty_input = "input is empty"
 
-let rec solve input () =
-  if input = "" then Error err_empty_input
-  else
-    let matrix = Matrix.M.of_string input in
-    let count_paper lst = List.length @@ List.filter (fun c -> c <> ".") lst in
-    let accessible_rolls_of_paper = ref 0 in
-    for y = 0 to Array.length matrix - 1 do
-      for x = 0 to Array.length matrix.(y) - 1 do
-        if matrix.(y).(x) = "." then ()
-        else
-          let neighbour_coords = Matrix.M.get_valid_neighbours matrix x y in
-          let neighbours =
-            List.map
-              (fun (x', y') -> Matrix.M.get matrix x' y')
-              neighbour_coords
-          in
-          let paper_count = count_paper neighbours in
-          let is_accessible = paper_count < 4 in
-          if is_accessible then
-            accessible_rolls_of_paper := !accessible_rolls_of_paper + 1 ;
-          print_iteration_debug_msg x y neighbour_coords neighbours paper_count
-            is_accessible
-      done
-    done ;
-    Ok !accessible_rolls_of_paper
+let rec count_accessible_rolls matrix =
+  let count_paper lst = List.length @@ List.filter (fun c -> c <> ".") lst in
+  let accessible_rolls_of_paper = ref 0 in
+  count_accessible_rolls_aux matrix count_paper accessible_rolls_of_paper ;
+  !accessible_rolls_of_paper
+
+and count_accessible_rolls_aux matrix count_paper accessible_rolls_of_paper =
+  for y = 0 to Array.length matrix - 1 do
+    for x = 0 to Array.length matrix.(y) - 1 do
+      if matrix.(y).(x) = "." then ()
+      else
+        let neighbour_coords = Matrix.M.get_valid_neighbours matrix x y in
+        let neighbours =
+          List.map (fun (x', y') -> Matrix.M.get matrix x' y') neighbour_coords
+        in
+        let paper_count = count_paper neighbours in
+        let is_accessible = paper_count < 4 in
+        if is_accessible then
+          accessible_rolls_of_paper := !accessible_rolls_of_paper + 1 ;
+        print_iteration_debug_msg x y neighbour_coords neighbours paper_count
+          is_accessible
+    done
+  done
 
 and print_iteration_debug_msg x y neighbour_coords neighbours paper_count
     is_accessible =
@@ -46,3 +44,10 @@ and print_iteration_debug_msg x y neighbour_coords neighbours paper_count
              if acc = "" then " " ^ neighbour ^ "; " else acc ^ neighbour ^ "; " )
            "" neighbours )
         paper_count is_accessible )
+
+let solve input () =
+  if input = "" then Error err_empty_input
+  else
+    let matrix = Matrix.M.of_string input in
+    let accessible_rolls_of_paper = count_accessible_rolls matrix in
+    Ok accessible_rolls_of_paper