d25

25/main.ml

@@ -0,0 +1,73 @@
+open Printf;;
+
+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 rec split_on_empty_line lines =
+  match lines with
+  | head :: tail ->
+    if String.length head = 0 then
+      ([], tail)
+    else
+      let rest_of_list, remaining_lines = split_on_empty_line tail in
+      (head :: rest_of_list, remaining_lines)
+  | _ -> ([], lines)
+
+let rec split_by_empty_lines lines =
+  if List.length lines = 0 then
+    []
+  else
+    let line, remainder = split_on_empty_line lines in
+    line :: split_by_empty_lines remainder
+
+let rec sum_columns_inner arr lst =
+  match lst with
+  | head :: tail ->
+    String.iteri (fun i v -> if v = '#' then arr.(i) <- arr.(i) + 1) head;
+    sum_columns_inner arr tail
+  | _ -> ()
+
+let sum_columns elem_len lst =
+  let arr = Array.make elem_len 0 in
+  sum_columns_inner arr lst;
+  Array.to_list arr
+
+let parse_schematic_fold (locks, keys) schematic =
+  match schematic with
+  | head :: tail -> begin
+    let heights = match (List.rev tail) with
+    | last :: rest ->
+      sum_columns (String.length head) rest
+    | _ -> raise (Invalid_argument "Invalid schematic") in
+    if head.[0] = '.' then
+      (locks, heights :: keys)
+    else
+      (heights :: locks, keys)
+  end
+  | _ -> raise (Invalid_argument "Invalid schematic")
+
+let rec heights_fit key lock =
+  match (key, lock) with
+  | (head1 :: tail1, head2:: tail2) ->
+    if head1 + head2 > 5 then 
+      false
+    else
+      heights_fit tail1 tail2
+  | ([], []) -> true
+  | _ -> raise (Invalid_argument "Key lengths don't match")
+
+let () =
+  let f = open_in "input.txt" in
+  let schematics = list_of_lines f |> split_by_empty_lines in
+  let locks, keys = List.fold_left parse_schematic_fold ([], []) schematics in
+  let result = locks |> List.map (fun lock ->
+    keys
+    |> List.map (fun key -> if heights_fit key lock then 1 else 0)
+    |> List.fold_left Int.add 0)
+  |> List.fold_left Int.add 0 in
+  printf "%d\n" result