From 09950d6097ea7b2590fb80336d144ee402e61226 Mon Sep 17 00:00:00 2001
From: Bama Charan Chhandogi <b.c.chhandogi@gmail.com>
Date: Sun, 3 Sep 2023 01:02:28 +0530
Subject: [PATCH] Add Rotate a Linkedlist (#4345)

---
 .../lists/RotateSinglyLinkedLists.java        | 33 +++++++++
 .../lists/RotateSinglyLinkedListsTest.java    | 72 +++++++++++++++++++
 2 files changed, 105 insertions(+)
 create mode 100644 src/main/java/com/thealgorithms/datastructures/lists/RotateSinglyLinkedLists.java
 create mode 100644 src/test/java/com/thealgorithms/datastructures/lists/RotateSinglyLinkedListsTest.java

diff --git a/src/main/java/com/thealgorithms/datastructures/lists/RotateSinglyLinkedLists.java b/src/main/java/com/thealgorithms/datastructures/lists/RotateSinglyLinkedLists.java
new file mode 100644
index 000000000..e7ea95d3f
--- /dev/null
+++ b/src/main/java/com/thealgorithms/datastructures/lists/RotateSinglyLinkedLists.java
@@ -0,0 +1,33 @@
+package com.thealgorithms.datastructures.lists;
+
+/**
+ * Rotate a list
+ * @author Bama Charan Chhandogi (https://github.com/BamaCharanChhandogi)
+ */
+
+public class RotateSinglyLinkedLists {
+    public Node rotateRight(Node head, int k) {
+        if (head == null || head.next == null || k == 0) {
+            return head;
+        }
+
+        Node curr = head;
+        int len = 1;
+        while (curr.next != null) {
+            curr = curr.next;
+            len++;
+        }
+
+        curr.next = head;
+        k = k % len;
+        k = len - k;
+        while (k > 0) {
+            curr = curr.next;
+            k--;
+        }
+
+        head = curr.next;
+        curr.next = null;
+        return head;
+    }
+}
diff --git a/src/test/java/com/thealgorithms/datastructures/lists/RotateSinglyLinkedListsTest.java b/src/test/java/com/thealgorithms/datastructures/lists/RotateSinglyLinkedListsTest.java
new file mode 100644
index 000000000..23780758b
--- /dev/null
+++ b/src/test/java/com/thealgorithms/datastructures/lists/RotateSinglyLinkedListsTest.java
@@ -0,0 +1,72 @@
+package com.thealgorithms.datastructures.lists;
+
+/**
+ * Test cases for RotateSinglyLinkedLists
+ * Author: Bama Charan Chhandogi (https://github.com/BamaCharanChhandogi)
+ */
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+
+public class RotateSinglyLinkedListsTest {
+
+    @Test
+    public void testRotateRightEmptyList() {
+        RotateSinglyLinkedLists rotator = new RotateSinglyLinkedLists();
+
+        // Test case: Rotate an empty list
+        assertNull(rotator.rotateRight(null, 2));
+    }
+
+    @Test
+    public void testRotateRightSingleNodeList() {
+        RotateSinglyLinkedLists rotator = new RotateSinglyLinkedLists();
+
+        // Test case: Rotate a list with one element
+        Node singleNode = new Node(5);
+        Node rotatedSingleNode = rotator.rotateRight(singleNode, 3);
+        assertEquals(5, rotatedSingleNode.value);
+        assertNull(rotatedSingleNode.next);
+    }
+
+    @Test
+    public void testRotateRightMultipleElementsList() {
+        RotateSinglyLinkedLists rotator = new RotateSinglyLinkedLists();
+
+        // Test case: Rotate a list with multiple elements (Rotate by 2)
+        Node head = new Node(1);
+        head.next = new Node(2);
+        head.next.next = new Node(3);
+        head.next.next.next = new Node(4);
+        head.next.next.next.next = new Node(5);
+
+        Node rotated1 = rotator.rotateRight(head, 2);
+        assertEquals(4, rotated1.value);
+        assertEquals(5, rotated1.next.value);
+        assertEquals(1, rotated1.next.next.value);
+        assertEquals(2, rotated1.next.next.next.value);
+        assertEquals(3, rotated1.next.next.next.next.value);
+        assertNull(rotated1.next.next.next.next.next);
+    }
+
+    @Test
+    public void testRotateRightFullRotation() {
+        RotateSinglyLinkedLists rotator = new RotateSinglyLinkedLists();
+
+        // Test case: Rotate a list with multiple elements (Full rotation)
+        Node head = new Node(1);
+        head.next = new Node(2);
+        head.next.next = new Node(3);
+        head.next.next.next = new Node(4);
+        head.next.next.next.next = new Node(5);
+
+        Node rotated3 = rotator.rotateRight(head, 7);
+        assertEquals(4, rotated3.value);
+        assertEquals(5, rotated3.next.value);
+        assertEquals(1, rotated3.next.next.value);
+        assertEquals(2, rotated3.next.next.next.value);
+        assertEquals(3, rotated3.next.next.next.next.value);
+        assertNull(rotated3.next.next.next.next.next);
+    }
+}