Improved solution for smelodesousa/F5/5-brackets (#40)

Close learn-ocaml-community/teaching-feedback#1

Co-authored-by: zazed <[email protected]>

exercises/smelodesousa/F5/5-brackets/descr.md

@@ -13,8 +13,8 @@ Note that, as a result, concatenating two texts with well-placed parentheses or
 
 # Goal
 
-Define a function `verify : char list -> char list -> bool` which checks if the text contained in the first parameter has well-placed parentheses. It is suggested that you use the second parameter (another `char list`, which we will define the accumulator) to _accumulate_ the intermediate scan results. Therefore, the accumulator is empty at the beginning of the analysis, and if during the check the accumulator has a parenthesis '(' as its first element, then the current status of the analysis still waits for a parenthesis ')'  which corresponds to the closing of the parenthesis in the accumulator. A proper use of this accumulator makes checking much easier!
+Define a function `verify : char list -> bool` that checks if the text contained in the first parameter has well-placed parentheses. If you aren't familiar with OCaml's list iterators, feel free to write a local function involving an accumulator to _accumulate_ the intermediate scan results. Therefore, the accumulator is empty at the beginning of the analysis, and if during the check the accumulator has a parenthesis '(' as its first element, then the current status of the analysis still waits for a parenthesis ')'  which corresponds to the closing of the parenthesis in the accumulator. Proper use of this accumulator makes checking much easier!
 
 For example:
 
-`verify ['a';'(';'a';'b';'(';'b';')';'c';'(';'o';'k';'a';')';'n';')';'h'] [] = true`
+`verify ['a';'(';'a';'b';'(';'b';')';'c';'(';'o';'k';'a';')';'n';')';'h'] = true`

exercises/smelodesousa/F5/5-brackets/meta.json

@@ -11,6 +11,10 @@
     [
       "Rui Barata",
       "[email protected]"
+    ],
+    [
+      "Leonardo Santos",
+      "[email protected]"
     ]
   ],
   "backward_exercises": [

exercises/smelodesousa/F5/5-brackets/solution.ml

@@ -1,12 +1,5 @@
-let verify text accumulator =
-  let clean_accumulator acc =
-    match acc with
-    | c1::c2::t -> if c1 = ')' && c2 = '(' then t else acc
-    | c1::[] -> acc
-    | [] -> acc in
-  let rec verify_aux text accumulator =
-    match text with 
-    | c::t when (c = '(' || c = ')') -> verify_aux t (clean_accumulator (c::accumulator))
-    | c::t when (c <> '(' || c <> ')')  -> verify_aux t accumulator
-    | [] -> accumulator in
-  (verify_aux text accumulator) = []
+let verify text =
+  List.fold_left
+    (fun acc c -> if acc < 0 then acc else match c with '(' -> acc + 1 | ')' -> acc - 1 | _ -> acc)
+    0 text
+  = 0

exercises/smelodesousa/F5/5-brackets/template.ml

@@ -1,2 +1,2 @@
-let verify text accumulator = 
+let verify text = 
   failwith "Replace with your solution"

exercises/smelodesousa/F5/5-brackets/test.ml

@@ -1,10 +1,8 @@
 open Test_lib
 open Report
 
-let sample_verify_right () = 
-  ([], [])
-let sample_verify_wrong () =
-  ([], [])
+let sample_verify_right () = []
+let sample_verify_wrong () = []
 
 let sample_verify () = 
   let () = Random.self_init () in
@@ -13,12 +11,12 @@ let sample_verify () =
   else sample_verify_wrong ()
 
 let verifyS () =
-  test_function_2_against_solution
-  [%ty: char list -> char list -> bool ]
+  test_function_1_against_solution
+  [%ty: char list -> bool ]
   "verify"
   ~sampler: sample_verify
   ~gen: 0
-  [(['a';'(';'a';'b';'(';'b';')';'c';'(';'o';'k';'a';')';'n';')';'h'], []); (['a';'(';'a';'b';'(';'b';')';'c';'(';'o';'k';'a';'n';')';'h'], [])]
+  [[')'; '(']; ['a';'(';'a';'b';'(';'b';')';'c';'(';'o';'k';'a';')';'n';')';'h']; ['a';'(';'a';'b';'(';'b';')';'c';'(';'o';'k';'a';'n';')';'h']]
 
 let () =
   set_result                @@