refactor: RotateListRight.js and added tests (TheAlgorithms#1101)

* Refactored RotatedListRight.js and added its tests * rotateListRight test and improved implementation * Review changes on constructor's loop

Author: 10kartik

Data-Structures/Linked-List/RotateListRight.js

@@ -6,7 +6,7 @@
 * a singly linked list.
 */
 
-// Methods - size, head, addLast, addFirst, addAt, removeFirst, removeLast, remove, removeAt, indexOf, isEmpty, elementAt, findMiddle, get, clean
+// Methods - size, head, addLast, addFirst, addAt, removeFirst, removeLast, remove, removeAt, indexOf, isEmpty, elementAt, findMiddle, get, clean, rotateListRight
 
 classNode{
 constructor(data){
@@ -16,9 +16,15 @@ class Node{
 }
 
 classLinkedList{
-constructor(){
+constructor(listOfValues){
 this.headNode=null
 this.length=0
+
+if(listOfValuesinstanceofArray){
+for(constvalueoflistOfValues){
+this.addLast(value)
+}
+}
 }
 
 // initiates the currentNode and currentIndex and return as an object
@@ -224,6 +230,32 @@ class LinkedList{
 returnlist
 }
 
+// Method for Rotating a List to the right by k places
+rotateListRight(k){
+leti=0
+letcurrent=this.headNode
+while(current){
+i++
+current=current.next
+}
+k%=i
+current=this.headNode
+letprev=null
+while(k--){
+if(!current||!current.next){
+returncurrent
+}else{
+while(current.next){
+prev=current
+current=current.next
+}
+prev.next=current.next
+current.next=this.headNode
+this.headNode=current
+}
+}
+}
+
 // Method to iterate over the LinkedList
 iterator(){
 let{ currentNode }=this.initiateNodeAndIndex()

Data-Structures/Linked-List/SinglyLinkedList.js

@@ -222,4 +222,29 @@ describe('SinglyLinkedList', () =>{
 list.clean()
 expect(list.isEmpty()).toBe(true)
 })
+
+it('should shift every node by k steps towards right, shifts tail nodes towards the start and change head of the list',()=>{
+// Case 0: When head of list is null
+consttempNode=newLinkedList()
+expect(tempNode.get()).toEqual([])
+
+// Creating list
+constheadNode=newLinkedList([10,20,30,40,50])
+
+// Case 1: when k = 0 => List should be unaffected
+headNode.rotateListRight(0)
+expect(headNode.get()).toEqual([10,20,30,40,50])
+
+// Case 2: Rotate right by 2 steps
+headNode.rotateListRight(2)
+expect(headNode.get()).toEqual([40,50,10,20,30])
+
+// Case 3: Rotate right by 12 steps
+headNode.rotateListRight(12)
+expect(headNode.get()).toEqual([20,30,40,50,10])
+
+// Case 4: when k = length of the list = 5 => List should be unaffected
+headNode.rotateListRight(5)
+expect(headNode.get()).toEqual([20,30,40,50,10])
+})
 })