Update solution for 2021 day 10

Generalize scoring function

2021/day-10/common.ml

@@ -19,3 +19,36 @@ let is_pair o c =
   | ('{', '}') -> true
   | ('<', '>') -> true
   | (_, _)     -> false
+
+let rec rem_score stack points =
+  let score ch =
+    match ch with
+    | '(' -> 1
+    | '[' -> 2
+    | '{' -> 3
+    | '<' -> 4
+    | _   -> 0
+  in
+
+  match stack with
+  | [] -> points
+  | x :: xs -> rem_score xs (points * 5 + (score x))
+
+let err_score ch =
+  match ch with
+  | ')' -> 3
+  | ']' -> 57
+  | '}' -> 1197
+  | '>' -> 25137
+  | _   -> 0
+
+
+let rec scores line stack error_score =
+  match (line, stack) with
+  | ([], _) -> (error_score, rem_score stack 0)
+  | (x :: xs, y :: ys) when is_closing x ->
+    if is_pair y x
+    then scores xs ys error_score
+    else scores xs ys (error_score + err_score x)
+  | (x :: xs, _) ->
+    scores xs (x :: stack) error_score

2021/day-10/part_one.ml

@@ -1,28 +1,13 @@
 open Common
 
-let score ch =
-  match ch with
-  | ')' -> 3
-  | ']' -> 57
-  | '}' -> 1197
-  | '>' -> 25137
-  | _   -> 0
-
-let rec count_errors line stack errors =
-  match (line, stack) with
-  | ([], _) -> errors
-  | (x :: xs, y :: ys) when is_closing x ->
-    if is_pair y x
-    then count_errors xs ys errors
-    else count_errors xs ys (errors + score x)
-  | (x :: xs, _) ->
-    count_errors xs (x :: stack) errors
-
 let () =
   let path = Sys.argv.(1) in
 
   read_file path
-  |> List.map (fun cs -> count_errors cs [] 0)
+  |> List.map (fun cs ->
+    match scores cs [] 0 with
+    | (e, _) -> e
+  )
   |> List.fold_left (+) 0
   |> print_int;
 

2021/day-10/part_two.ml

@@ -1,33 +1,14 @@
 open Common
 
-let score ch =
-  match ch with
-  | '(' -> 1
-  | '[' -> 2
-  | '{' -> 3
-  | '<' -> 4
-  | _   -> 0
-
-let rec score_remaining stack points =
-  match stack with
-  | [] -> points
-  | x :: xs -> score_remaining xs (points * 5 + (score x))
-
-let rec score_closing line stack =
-  match (line, stack) with
-  | ([], _) -> Some (score_remaining stack 0)
-  | (x :: xs, y :: ys) when is_closing x ->
-    if is_pair y x
-    then score_closing xs ys
-    else None
-  | (x :: xs, _) ->
-    score_closing xs (x :: stack)
-
 let () =
   let path = Sys.argv.(1) in
 
   read_file path
-  |> List.filter_map (fun cs -> score_closing cs [])
+  |> List.filter_map (fun cs ->
+    match scores cs [] 0 with
+    | (0, r) -> Some(r)
+    | (_, _) -> None
+  )
   |> List.sort compare
   |> fun lst -> List.nth lst (List.length lst / 2)
   |> print_int;