day 5 part 1

5/main.ml

@@ -0,0 +1,77 @@
+open Printf;;
+open String;;
+open Map;;
+
+let rec list_of_lines in_file =
+  try
+    let line = input_line in_file in
+    line :: list_of_lines(in_file)
+  with End_of_file ->
+    close_in in_file;
+    []
+
+let is_not_empty lst = 
+  match lst with
+  | [] -> false 
+  | _  -> true
+
+let rec parse_int_list sep str =
+  let list1 = (List.filter (fun a -> length a != 0) (String.split_on_char sep str)) in
+  List.map int_of_string list1
+
+module IntMap = Map.Make(Int)
+module IntSet = Set.Make(Int)
+
+let rec parse_ordering lines must_be_before =
+  match lines with
+  | head :: tail ->
+    if length head > 0 then
+      let elems = parse_int_list '|' head in
+      let e1 = List.hd elems in
+      let e2 = List.nth elems 1 in
+      let update_fun prev =
+        match prev with 
+        | Some set -> Some (IntSet.add e1 set)
+        | None -> Some (IntSet.add e1 IntSet.empty) in
+      let new_map = IntMap.update e2 update_fun must_be_before in
+      parse_ordering tail new_map
+    else 
+      (tail, must_be_before)
+  | _ -> (lines, must_be_before)
+
+let parse in_file =
+  let lines = list_of_lines in_file in
+  let lines_rest, must_be_before = parse_ordering lines IntMap.empty in
+  let entries = List.map (fun str -> List.rev @@ parse_int_list ',' str) lines_rest in
+  (must_be_before, entries)
+
+let rec is_good must_be_before already_appeared entry =
+  match entry with
+  | head :: tail -> begin
+    let new_already_appeared = IntSet.add head already_appeared in
+    match IntMap.find_opt head must_be_before with
+    | Some set ->
+      let intersect = IntSet.inter set new_already_appeared in
+      if IntSet.is_empty intersect then
+        is_good must_be_before new_already_appeared tail
+      else
+        false
+    | None ->
+      is_good must_be_before new_already_appeared tail
+    end
+  | _ -> true
+
+let rec summarise_good_entries must_be_before entries =
+  match entries with
+  | head :: tail ->
+    if is_good must_be_before IntSet.empty head then
+      List.nth head (List.length head / 2) + summarise_good_entries must_be_before tail
+    else
+      summarise_good_entries must_be_before tail
+  | _ -> 0
+
+let () =
+  let f = open_in "input.txt" in
+  let must_be_before, entries = parse f in
+  let result = summarise_good_entries must_be_before entries in
+  printf "%d\n" result