Merge pull request PrajaktaSathe#153 from btdo/RotateLinkedList

New program to demonstrate rotating singly linked list

Author: PrajaktaSathe

Programs/RotateLinkedList.java

@@ -0,0 +1,122 @@
+import java.util.*;
+
+/**
+ * Definition for singly-linked list.
+ **/
+class SinglyLinkedNode {
+ int val;
+ SinglyLinkedNode next;
+
+ public SinglyLinkedNode(int val) {
+ this.val = val;
+ }
+}
+
+/**
+ * This is a program to demo rotating a singly linked list.
+ * @see <a href=
+ * "https://leetcode.com/problems/rotate-list/description/">LeetCode
+ * description</a>
+ * Time complexity O(n), Space O(1)
+ */
+public class RotateLinkedList {
+ public static void main(String[] args) {
+ try (Scanner sc = new Scanner(System.in)) {
+ System.out.println("Enter the LinkedList in the form of [1,2,3,4,5]");
+ String input = sc.nextLine();
+ System.out.println("Enter the number of rotations");
+ int k = sc.nextInt();
+ String str = input.replaceAll(" ", "") .substring(1, input.length() - 1);
+ String[] nodesStr = str.split(",");
+ if (nodesStr.length == 0) {
+ System.out.println("[]");
+ return;
+ }
+
+ SinglyLinkedNode head = buildLinkedList(nodesStr);
+ RotateLinkedList solution = new RotateLinkedList();
+ SinglyLinkedNode newHead = solution.rotateRight(head, k);
+ printOutput(newHead);
+ } catch (Exception e) {
+ System.out.println(
+ "Something went wrong. Check the linkedlist format is in the form of [1,2,3,4,5] and rotation is an integer");
+ }
+ }
+
+ private static SinglyLinkedNode buildLinkedList(String[] nodesStr) {
+ SinglyLinkedNode head = null;
+ SinglyLinkedNode node = null;
+ for (int i = 0; i < nodesStr.length; i++) {
+ SinglyLinkedNode newNode = new SinglyLinkedNode(Integer.valueOf(nodesStr[i]));
+ if (i == 0) {
+ head = newNode;
+ }
+
+ if (node == null) {
+ node = newNode;
+ } else {
+ node.next = newNode;
+ node = newNode;
+ }
+ }
+
+ return head;
+ }
+
+ private static void printOutput(SinglyLinkedNode newHead) {
+ System.out.print("[");
+ do {
+ System.out.print(newHead.val);
+ newHead = newHead.next;
+ if (newHead != null) {
+ System.out.print(",");
+ }
+ } while(newHead != null);
+ System.out.println("]");
+ }
+
+ /**
+ * Given the head of a linked list, rotate the list to the right by k places.
+ * @param head
+ * @param k
+ * @return head of linked list
+ */
+ public SinglyLinkedNode rotateRight(SinglyLinkedNode head, int k) {
+ if (k == 0 || head == null || head.next == null) {
+ return head;
+ }
+
+ // Finding the size of the list
+ int size = 1; // start with 1 because we're starting with head
+ SinglyLinkedNode currentEnd = head;
+ while (currentEnd.next != null) {
+ currentEnd = currentEnd.next;
+ size++;
+ }
+
+ // linking the end to the head
+ currentEnd.next = head;
+
+ // determine the rotation based on k
+ int rotate = 0;
+ if (k < size) {
+ rotate = k;
+ } else {
+ rotate = k % size;
+ }
+
+ // Find the index of the end node
+ int endNode = size - rotate;
+
+ // set the newEnd to head and loop until you get to the new end node
+ SinglyLinkedNode newEnd = head;
+ for (int i = 1; i < endNode; i++) {
+ newEnd = newEnd.next;
+ }
+
+ // set the new head node and terminate the new end node
+ SinglyLinkedNode newHead = newEnd.next;
+ newEnd.next = null;
+ return newHead;
+ }
+}

README.md

@@ -123,6 +123,7 @@ It is very easy to contribute, you may follow these steps -
 96. [Xor Palindrome](https://github.com/PrajaktaSathe/Java/blob/main/Programs/Xorpalindrome.java) - Program/Solution to Xor Palindrome
 97. [Streams API](./Programs/JavaStreams.java) - Program to demo the Java Stream API with String and Integer Lists.
 98.[Stack](https://github.com/PrajaktaSathe/Java/blob/main/Stack.java)-Program to demo the stack implementation
+99.[RotateLinkedList](https://github.com/PrajaktaSathe/Java/blob/main/Programs/RotateLinkedList.java)-Program to demo rotating a linked list
 # Contributors - 
 ## A big thank you to all our contributors!!!