style: enable MissingSwitchDefault in checkstyle (#5179)

* Update directory

* Update directory

* Update directory

* Update directory

* add switch default

---------

Co-authored-by: BamaCharanChhandogi <BamaCharanChhandogi@users.noreply.github.com>

src/main/java/com/thealgorithms/strings/ValidParentheses.java

@@ -26,6 +26,8 @@ public final class ValidParentheses {
             case ']':
                 if (head == 0 || stack[--head] != '[') return false;
                 break;
+            default:
+                throw new IllegalArgumentException("Unexpected character: " + c);
             }
         }
         return head == 0;