From 6d8f87bb87262a522dfc2c54c0f4bc3433df053b Mon Sep 17 00:00:00 2001
From: alxkm <alexanderklmn@gmail.com>
Date: Mon, 7 Jul 2025 23:55:00 +0200
Subject: [PATCH 1/3] refactor: optimize ValidParentheses methods and add
 parameterized tests

---
 .../strings/ValidParentheses.java             | 88 +++++++++----------
 .../strings/ValidParenthesesTest.java         | 29 +++---
 2 files changed, 55 insertions(+), 62 deletions(-)

diff --git a/src/main/java/com/thealgorithms/strings/ValidParentheses.java b/src/main/java/com/thealgorithms/strings/ValidParentheses.java
index 629fee495d84..c78d0d4e9730 100644
--- a/src/main/java/com/thealgorithms/strings/ValidParentheses.java
+++ b/src/main/java/com/thealgorithms/strings/ValidParentheses.java
@@ -1,59 +1,57 @@
 package com.thealgorithms.strings;
-//        Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine
-//        if the input string is valid. An input string is valid if: Open brackets must be closed by
-//        the same type of brackets. Open brackets must be closed in the correct order. Every close
-//        bracket has a corresponding open bracket of the same type.
 
+import java.util.ArrayDeque;
+import java.util.Deque;
+import java.util.Map;
+
+/**
+ * Validates if a given string has valid matching parentheses.
+ * <p>
+ * A string is considered valid if:
+ * <ul>
+ *     <li>Open brackets are closed by the same type of brackets.</li>
+ *     <li>Brackets are closed in the correct order.</li>
+ *     <li>Every closing bracket has a corresponding open bracket of the same type.</li>
+ * </ul>
+ *
+ * Allowed characters: '(', ')', '{', '}', '[', ']'
+ */
 public final class ValidParentheses {
     private ValidParentheses() {
     }
+
+    private static final Map<Character, Character> BRACKET_PAIRS = Map.of(
+            ')', '(',
+            '}', '{',
+            ']', '['
+    );
+
+    /**
+     * Checks if the input string has valid parentheses.
+     *
+     * @param s the string containing only bracket characters
+     * @return true if valid, false otherwise
+     * @throws IllegalArgumentException if the string contains invalid characters or is null
+     */
     public static boolean isValid(String s) {
-        char[] stack = new char[s.length()];
-        int head = 0;
+        if (s == null) {
+            throw new IllegalArgumentException("Input string cannot be null");
+        }
+
+        Deque<Character> stack = new ArrayDeque<>();
+
         for (char c : s.toCharArray()) {
-            switch (c) {
-            case '{':
-            case '[':
-            case '(':
-                stack[head++] = c;
-                break;
-            case '}':
-                if (head == 0 || stack[--head] != '{') {
-                    return false;
-                }
-                break;
-            case ')':
-                if (head == 0 || stack[--head] != '(') {
-                    return false;
-                }
-                break;
-            case ']':
-                if (head == 0 || stack[--head] != '[') {
+            if (BRACKET_PAIRS.containsValue(c)) {
+                stack.push(c); // opening bracket
+            } else if (BRACKET_PAIRS.containsKey(c)) {
+                if (stack.isEmpty() || stack.pop() != BRACKET_PAIRS.get(c)) {
                     return false;
                 }
-                break;
-            default:
-                throw new IllegalArgumentException("Unexpected character: " + c);
-            }
-        }
-        return head == 0;
-    }
-    public static boolean isValidParentheses(String s) {
-        int i = -1;
-        char[] stack = new char[s.length()];
-        String openBrackets = "({[";
-        String closeBrackets = ")}]";
-        for (char ch : s.toCharArray()) {
-            if (openBrackets.indexOf(ch) != -1) {
-                stack[++i] = ch;
             } else {
-                if (i >= 0 && openBrackets.indexOf(stack[i]) == closeBrackets.indexOf(ch)) {
-                    i--;
-                } else {
-                    return false;
-                }
+                throw new IllegalArgumentException("Unexpected character: " + c);
             }
         }
-        return i == -1;
+
+        return stack.isEmpty();
     }
 }
diff --git a/src/test/java/com/thealgorithms/strings/ValidParenthesesTest.java b/src/test/java/com/thealgorithms/strings/ValidParenthesesTest.java
index 2b6884c91c8f..a95f23fad751 100644
--- a/src/test/java/com/thealgorithms/strings/ValidParenthesesTest.java
+++ b/src/test/java/com/thealgorithms/strings/ValidParenthesesTest.java
@@ -1,27 +1,22 @@
 package com.thealgorithms.strings;
 
-import static org.junit.jupiter.api.Assertions.assertFalse;
-import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
-import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
 
-public class ValidParenthesesTest {
+import java.util.stream.Stream;
 
-    @Test
-    void testOne() {
-        assertTrue(ValidParentheses.isValid("()"));
-        assertTrue(ValidParentheses.isValidParentheses("()"));
-    }
+public class ValidParenthesesTest {
 
-    @Test
-    void testTwo() {
-        assertTrue(ValidParentheses.isValid("()[]{}"));
-        assertTrue(ValidParentheses.isValidParentheses("()[]{}"));
+    @ParameterizedTest(name = "Input: \"{0}\" → Expected: {1}")
+    @MethodSource("parenthesesProvider")
+    void testIsValid(String input, boolean expected) {
+        assertEquals(expected, ValidParentheses.isValid(input));
     }
 
-    @Test
-    void testThree() {
-        assertFalse(ValidParentheses.isValid("(]"));
-        assertFalse(ValidParentheses.isValidParentheses("(]"));
+    static Stream<Arguments> parenthesesProvider() {
+        return Stream.of(Arguments.of("()", true), Arguments.of("()[]{}", true), Arguments.of("(]", false), Arguments.of("{[]}", true), Arguments.of("([{}])", true), Arguments.of("([)]", false), Arguments.of("", true), Arguments.of("(", false), Arguments.of(")", false));
     }
 }

From cc6e0e1f34eed230bad3ab46c5943885dcdaabd6 Mon Sep 17 00:00:00 2001
From: alxkm <alexanderklmn@gmail.com>
Date: Mon, 7 Jul 2025 23:57:08 +0200
Subject: [PATCH 2/3] refactor: fix clang formatting issues

---
 .../java/com/thealgorithms/strings/ValidParentheses.java    | 6 +-----
 .../com/thealgorithms/strings/ValidParenthesesTest.java     | 3 +--
 2 files changed, 2 insertions(+), 7 deletions(-)

diff --git a/src/main/java/com/thealgorithms/strings/ValidParentheses.java b/src/main/java/com/thealgorithms/strings/ValidParentheses.java
index c78d0d4e9730..25a72f379dec 100644
--- a/src/main/java/com/thealgorithms/strings/ValidParentheses.java
+++ b/src/main/java/com/thealgorithms/strings/ValidParentheses.java
@@ -20,11 +20,7 @@ public final class ValidParentheses {
     private ValidParentheses() {
     }
 
-    private static final Map<Character, Character> BRACKET_PAIRS = Map.of(
-            ')', '(',
-            '}', '{',
-            ']', '['
-    );
+    private static final Map<Character, Character> BRACKET_PAIRS = Map.of(')', '(', '}', '{', ']', '[');
 
     /**
      * Checks if the input string has valid parentheses.
diff --git a/src/test/java/com/thealgorithms/strings/ValidParenthesesTest.java b/src/test/java/com/thealgorithms/strings/ValidParenthesesTest.java
index a95f23fad751..cc2aae30053a 100644
--- a/src/test/java/com/thealgorithms/strings/ValidParenthesesTest.java
+++ b/src/test/java/com/thealgorithms/strings/ValidParenthesesTest.java
@@ -2,12 +2,11 @@
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
+import java.util.stream.Stream;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.Arguments;
 import org.junit.jupiter.params.provider.MethodSource;
 
-import java.util.stream.Stream;
-
 public class ValidParenthesesTest {
 
     @ParameterizedTest(name = "Input: \"{0}\" → Expected: {1}")

From 2588cdcbce609574672f58c742db719bbfcbed36 Mon Sep 17 00:00:00 2001
From: alxkm <alexanderklmn@gmail.com>
Date: Tue, 8 Jul 2025 00:18:45 +0200
Subject: [PATCH 3/3] refactor: fix spotbugs issue

---
 .../thealgorithms/strings/ValidParenthesesTest.java    | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/src/test/java/com/thealgorithms/strings/ValidParenthesesTest.java b/src/test/java/com/thealgorithms/strings/ValidParenthesesTest.java
index cc2aae30053a..23d41b159fe2 100644
--- a/src/test/java/com/thealgorithms/strings/ValidParenthesesTest.java
+++ b/src/test/java/com/thealgorithms/strings/ValidParenthesesTest.java
@@ -2,20 +2,14 @@
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
-import java.util.stream.Stream;
 import org.junit.jupiter.params.ParameterizedTest;
-import org.junit.jupiter.params.provider.Arguments;
-import org.junit.jupiter.params.provider.MethodSource;
+import org.junit.jupiter.params.provider.CsvSource;
 
 public class ValidParenthesesTest {
 
     @ParameterizedTest(name = "Input: \"{0}\" → Expected: {1}")
-    @MethodSource("parenthesesProvider")
+    @CsvSource({"'()', true", "'()[]{}', true", "'(]', false", "'{[]}', true", "'([{}])', true", "'([)]', false", "'', true", "'(', false", "')', false"})
     void testIsValid(String input, boolean expected) {
         assertEquals(expected, ValidParentheses.isValid(input));
     }
-
-    static Stream<Arguments> parenthesesProvider() {
-        return Stream.of(Arguments.of("()", true), Arguments.of("()[]{}", true), Arguments.of("(]", false), Arguments.of("{[]}", true), Arguments.of("([{}])", true), Arguments.of("([)]", false), Arguments.of("", true), Arguments.of("(", false), Arguments.of(")", false));
-    }
 }

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