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
 
 class Node {
  constructor (data) {
@@ -16,9 +16,15 @@ class Node {
 }
 
 class LinkedList {
- constructor () {
+ constructor (listOfValues) {
  this.headNode = null
  this.length = 0
+
+ if (listOfValues instanceof Array) {
+ for (const value of listOfValues) {
+ this.addLast(value)
+ }
+ }
  }
 
  // initiates the currentNode and currentIndex and return as an object
@@ -224,6 +230,32 @@ class LinkedList {
  return list
  }
 
+ // Method for Rotating a List to the right by k places
+ rotateListRight (k) {
+ let i = 0
+ let current = this.headNode
+ while (current) {
+ i++
+ current = current.next
+ }
+ k %= i
+ current = this.headNode
+ let prev = null
+ while (k--) {
+ if (!current || !current.next) {
+ return current
+ } 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
+ const tempNode = new LinkedList()
+ expect(tempNode.get()).toEqual([])
+
+ // Creating list
+ const headNode = new LinkedList([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])
+ })
 })