Day 5!

AdventOfCode2024/bin/main.ml

@@ -13,7 +13,7 @@ let read_lines name =
 let () =
   print_endline "\nAdvent of Code 2024";
   let part1, part2 =
-    read_lines "./inputs/04.txt" |> AdventOfCode2024.Day_04.solve
+    read_lines "./inputs/05.txt" |> AdventOfCode2024.Day_05.solve
   in
   Printf.printf "Part 1: %s\nPart 2: %s\n" (string_of_int part1)
     (string_of_int part2)

AdventOfCode2024/lib/day_05.ml

@@ -0,0 +1,120 @@
+module IntMap = Map.Make (Int)
+
+let rec print_list l =
+  match l with
+  | [] -> print_endline ""
+  | head :: tail ->
+      print_int head;
+      print_string ",";
+      print_list tail
+
+let option_to_val op =
+  match op with None -> raise (Invalid_argument "assertion") | Some v -> v
+
+let sublist list low high = List.filteri (fun i _ -> i >= low && i < high) list
+
+let add_rule_to_map (m : int list IntMap.t) rule =
+  let num1, num2 = Scanf.sscanf rule "%d|%d" (fun n1 n2 -> (n2, n1)) in
+  let existing_rules =
+    IntMap.update num1
+      (fun l ->
+        match l with
+        | None -> Some [ num2 ]
+        | Some existing_rules -> Some ([ num2 ] @ existing_rules))
+      m
+  in
+  existing_rules
+
+(*
+4 | 2
+2 | 3
+
+1, 2, 3 
+  /\
+
+prev_list = [1]
+pages_needed = [4, 7]
+
+ *)
+
+let rec is_sublist main_list sub_list =
+  match sub_list with
+  | [] -> true
+  | head :: tail ->
+      if List.exists (fun i -> head == i) main_list then
+        is_sublist main_list tail
+      else false
+
+let is_case_valid m case =
+  let rec loop prev_pages remaining_pages =
+    match remaining_pages with
+    | [] -> true
+    | head :: tail -> (
+        let pages_needed_before = IntMap.find_opt head m in
+        match pages_needed_before with
+        | None -> loop ([ head ] @ prev_pages) tail
+        | Some l ->
+            if
+              is_sublist prev_pages
+                (List.filter (fun i -> List.exists (fun j -> j == i) case) l)
+            then loop ([ head ] @ prev_pages) tail
+            else false)
+  in
+  loop [] case
+
+let partial_sort m case =
+  List.sort
+    (fun i j ->
+      let pages_needed_i = IntMap.find_opt i m in
+      let pages_needed_j = IntMap.find_opt j m in
+
+      match (pages_needed_i, pages_needed_j) with
+      | None, None -> 0
+      | Some _, None -> 1
+      | None, Some _ -> -1
+      | Some pages_i, Some _ ->
+          if List.exists (fun i -> i == j) pages_i then 1 else -1)
+    case
+
+let solve lines =
+  let rule_map : int list IntMap.t = IntMap.empty in
+
+  let empty_index =
+    List.find_index (fun i -> String.length i == 0) lines |> option_to_val
+  in
+  let rules = sublist lines 0 empty_index in
+  let cases = sublist lines (empty_index + 1) (List.length lines) in
+  let string_cases =
+    List.fold_left
+      (fun acc case ->
+        [ String.split_on_char ',' case |> List.map int_of_string ] @ acc)
+      [] cases
+  in
+
+  let map_with_rules = List.fold_left add_rule_to_map rule_map rules in
+  let is_case_valid_with_map = is_case_valid map_with_rules in
+
+  let part1 =
+    List.fold_left
+      (fun acc case ->
+        if is_case_valid_with_map case then
+          acc + List.nth case (List.length case / 2)
+        else acc)
+      0 string_cases
+  in
+
+  let invalid_cases =
+    List.filter (fun case -> is_case_valid_with_map case == false) string_cases
+  in
+
+  let sorted_invalid_cases =
+    List.map (fun case -> partial_sort map_with_rules case) invalid_cases
+  in
+
+  let part2 =
+    List.fold_left
+      (fun acc case -> acc + List.nth case (List.length case / 2))
+      0 sorted_invalid_cases
+  in
+
+  (part1, part2)