refactor: RotateListRight.js and added tests (#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])
+  })
 })