fix: update ValidParentheses and tests for coverage & formatting

Author: Ruturaj-007

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

@@ -13,9 +13,7 @@ private ValidParentheses() {
         throw new AssertionError("Cannot instantiate utility class");
     }
 
-    private static final Map<Character, Character> PAIRS = Map.of(
-            ')', '(', '}', '{', ']', '['
-    );
+    private static final Map<Character, Character> PAIRS = Map.of(')', '(', '}', '{', ']', '[');
 
     /**
      * Checks if the input string has valid parentheses.
@@ -24,18 +22,13 @@ private ValidParentheses() {
      * @return true if valid, false otherwise
      */
     public static boolean isValid(final String s) {
-        if (s == null) {
-            throw new NullPointerException("Input cannot be null");
-        }
-
+        if (s == null) throw new NullPointerException("Input cannot be null");
         Deque<Character> stack = new ArrayDeque<>();
         for (char ch : s.toCharArray()) {
-            if (PAIRS.containsValue(ch)) { // opening bracket
+            if (PAIRS.containsValue(ch)) {
                 stack.push(ch);
-            } else if (PAIRS.containsKey(ch)) { // closing bracket
-                if (stack.isEmpty() || stack.pop() != PAIRS.get(ch)) {
-                    return false;
-                }
+            } else if (PAIRS.containsKey(ch)) {
+                if (stack.isEmpty() || stack.pop() != PAIRS.get(ch)) return false;
             }
         }
         return stack.isEmpty();

src/test/java/com/thealgorithms/stacks/ValidParenthesesTest.java

@@ -12,32 +12,19 @@
 public class ValidParenthesesTest {
 
     @ParameterizedTest
-    @CsvSource({
-            "'()', true",
-            "'()[]{}', true",
-            "'{[]}', true",
-            "'', true"
-    })
+    @CsvSource({"'()', true", "'()[]{}', true", "'{[]}', true", "'', true"})
     void testValidParentheses(String input, boolean expected) {
         assertEquals(expected, ValidParentheses.isValid(input));
     }
 
     @ParameterizedTest
-    @CsvSource({
-            "'(', false",
-            "')', false",
-            "'([)]', false",
-            "'{[}]', false",
-            "'((()', false"
-    })
+    @CsvSource({"'(', false", "')', false", "'([)]', false", "'{[}]', false", "'((()', false"})
     void testInvalidParentheses(String input, boolean expected) {
         assertEquals(expected, ValidParentheses.isValid(input));
     }
 
     @ParameterizedTest
-    @CsvSource({
-            "null"
-    })
+    @CsvSource({"null"})
     void testNullInput(String input) {
         assertThrows(NullPointerException.class, () -> ValidParentheses.isValid(null));
     }