Add ReverseStringUsingStack

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

@@ -0,0 +1,34 @@
+package com.thealgorithms.stacks;
+
+import java.util.Stack;
+
+public final class ReverseStringUsingStack {
+    private ReverseStringUsingStack() {
+    }
+
+    /**
+     * @param str string to be reversed using stack
+     * @return reversed string
+     */
+    public static String reverse(String str) {
+        // Check if the input string is null
+        if (str == null) {
+            throw new IllegalArgumentException("Input string cannot be null");
+        }
+        Stack<Character> stack = new Stack<>();
+        StringBuilder reversedString = new StringBuilder();
+        // Check if the input string is empty
+        if (str.isEmpty()) {
+            return str;
+        }
+        // Push each character of the string onto the stack
+        for (char ch : str.toCharArray()) {
+            stack.push(ch);
+        }
+        // Pop each character from the stack and append to the StringBuilder
+        while (!stack.isEmpty()) {
+            reversedString.append(stack.pop());
+        }
+        return reversedString.toString();
+    }
+}

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

@@ -1,5 +1,7 @@
 package com.thealgorithms.strings;
 
+import java.util.Stack;
+
 /**
  * Reverse String using different version
  */
@@ -57,4 +59,31 @@ public static String reverse3(String string) {
         }
         return sb.toString();
     }
+    /**
+     * Reverses the given string using a stack.
+     * This method uses a stack to reverse the characters of the string.
+     * * @param str The input string to be reversed.
+     * @return The reversed string.
+     */
+    public static String reverse4(String str) {
+        // Check if the input string is null
+        if (str == null) {
+            throw new IllegalArgumentException("Input string cannot be null");
+        }
+        Stack<Character> stack = new Stack<>();
+        StringBuilder reversedString = new StringBuilder();
+        // Check if the input string is empty
+        if (str.isEmpty()) {
+            return str;
+        }
+        // Push each character of the string onto the stack
+        for (char ch : str.toCharArray()) {
+            stack.push(ch);
+        }
+        // Pop each character from the stack and append to the StringBuilder
+        while (!stack.isEmpty()) {
+            reversedString.append(stack.pop());
+        }
+        return reversedString.toString();
+    }
 }

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

@@ -0,0 +1,44 @@
+package com.thealgorithms.stacks;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import org.junit.jupiter.api.Test;
+
+class ReverseStringUsingStackTest {
+
+    @Test
+    void testRegularString() {
+        assertEquals("olleh", ReverseStringUsingStack.reverse("hello"));
+    }
+
+    @Test
+    void testEmptyString() {
+        assertEquals("", ReverseStringUsingStack.reverse(""));
+    }
+
+    @Test
+    void testPalindromeString() {
+        assertEquals("madam", ReverseStringUsingStack.reverse("madam"));
+    }
+
+    @Test
+    void testSpecialCharacters() {
+        assertEquals("#@!321cba", ReverseStringUsingStack.reverse("abc123!@#"));
+    }
+
+    @Test
+    void testSingleCharacter() {
+        assertEquals("x", ReverseStringUsingStack.reverse("x"));
+    }
+
+    @Test
+    void testWhitespaceHandling() {
+        assertEquals("dlroW olleH", ReverseStringUsingStack.reverse("Hello World"));
+    }
+
+    @Test
+    void testNullInput() {
+        assertThrows(IllegalArgumentException.class, () -> { ReverseStringUsingStack.reverse(null); });
+    }
+}

src/test/java/com/thealgorithms/strings/ReverseStringTest.java

@@ -1,8 +1,10 @@
 package com.thealgorithms.strings;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 
 import java.util.stream.Stream;
+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;
@@ -31,4 +33,15 @@ public void testReverseString2(String input, String expectedOutput) {
     public void testReverseString3(String input, String expectedOutput) {
         assertEquals(expectedOutput, ReverseString.reverse3(input));
     }
+
+    @ParameterizedTest
+    @MethodSource("testCases")
+    public void testReverseString4(String input, String expectedOutput) {
+        assertEquals(expectedOutput, ReverseString.reverse4(input));
+    }
+
+    @Test
+    public void testReverseString4WithNullInput() {
+        assertThrows(IllegalArgumentException.class, () -> ReverseString.reverse4(null));
+    }
 }