Solution day 5 part 1

5/solve_1.ml

@@ -15,7 +15,46 @@ let read_input =
   aux [] []
 ;;
 
-let rules = (fst read_input)
+let rules_graph = (fst read_input)
 let updates = (snd read_input)
 
-let () = List.iter (fun x -> printf "(%d, %d)\n" (fst x) (snd x)) rules
+let neighbors a = 
+  let aux g a =
+    let edge l (b, c) = if b = a then (c,'a') :: l
+                        else if c = a then (b,'b') :: l
+                        else l in
+    List.fold_left edge [] g in
+  aux rules_graph a
+;;
+
+let rec get_order nei = function
+| (n,o)::tl -> if (nei == n) then o else get_order nei tl
+| [] -> 'u'
+;;
+
+let rec is_page_ordered neighbors_p = function
+| [] -> true
+| hd :: tl -> if ((get_order hd neighbors_p) == 'a') then 
+                is_page_ordered neighbors_p tl else false
+;;   
+
+let get_middle_page u = let u_len = List.length u in List.nth u (u_len/2);;
+
+let solve =
+  let rec is_valid_update u = 
+    match u with
+    | hd :: tl -> 
+      (let hd_neighbors = neighbors hd in
+        if (is_page_ordered hd_neighbors tl) then (is_valid_update tl) else false
+      )
+    | [] -> true
+  in
+  let rec aux accum = function
+  | [] -> accum
+  | hd::tl -> if (is_valid_update hd) then aux (accum + get_middle_page hd) tl
+                                      else aux accum tl in
+  aux 0 updates
+;;
+
+
+let () = printf "Total: %d\n" solve

README.md

@@ -46,7 +46,7 @@ replace `<part_number>` with 1 for Part 1 or 2 for Part 2
 | 2   | ✅     | ✅     |
 | 3   | ✅     | ✅     |
 | 4   | ✅     | ✅     |
-| 5   | ⬜     | ⬜     |
+| 5   | ✅     | ⬜     |
 | 6   | ⬜     | ⬜     |
 | 7   | ⬜     | ⬜     |
 | 8   | ⬜     | ⬜     |