Sep 15, 2022 · Sep 13, 2022
diff --git a/Data-Structures/Linked-List/CycleDetection.js b/Data-Structures/Linked-List/CycleDetection.js
 /**
 * A LinkedList based solution forDetect a Cycle in a list
 * A LinkedList based solution forDetecting a Cycle in a list.
 * https://en.wikipedia.org/wiki/Cycle_detection
 */

 functionmain () {
 functiondetectCycle (head) {
  /*
  Problem Statement:
  Given head, the head of a linked list, determine if the linked list has a cycle in it.

  Note:
  * While Solving the problem in given link below, don't use main() function.
  * Just use only the code inside main() function.
  * The purpose of using main() function here is to avoid global variables.

  Link for the Problem: https://leetcode.com/problems/linked-list-cycle/
  */
  const head = '' // Reference to head is given in the problem. So please ignore this line
  let fast = head
  let slow = head
  if (!head) { return false }

  while (fast != null && fast.next != null && slow != null) {
  let slow = head
  let fast = head.next
  while (fast && fast.next) {
    if (fast === slow) { return true }
    fast = fast.next.next
    slow = slow.next
    if (fast === slow) {
      return true
    }
  }
  return false
 }

 main()
 export { detectCycle }
diff --git a/Data-Structures/Linked-List/test/CycleDetection.test.js b/Data-Structures/Linked-List/test/CycleDetection.test.js
 import { detectCycle } from '../CycleDetection'
 import { Node } from '../SinglyLinkedList'

 describe('Detect Cycle', () => {
  it('should detect loop and return true', () => {
    // Creating list and making a loop
    const headNode = new Node(10)
    headNode.next = new Node(20)
    headNode.next.next = new Node(30)
    headNode.next.next.next = new Node(40)
    headNode.next.next.next.next = headNode
    expect(detectCycle(headNode)).toEqual(true)
  })

  it('should not detect a loop and return false', () => {
    // Case 0: When head is null, there is no loop.
    expect(detectCycle(null)).toEqual(false)
    const headNode = new Node(10)

    // Case 1: List with single node doesn't have any loop
    expect(detectCycle(headNode)).toEqual(false)

    headNode.next = new Node(20)
    headNode.next.next = new Node(30)
    headNode.next.next.next = new Node(40)
    headNode.next.next.next.next = new Node(50)

    // Case 2: List not having any loops
    expect(detectCycle(headNode)).toEqual(false)
  })
 })
Original file line number	Diff line number	Diff line change
		@@ -1,32 +1,24 @@
		/**
		* A LinkedList based solution forDetect a Cycle in a list
		* A LinkedList based solution forDetecting a Cycle in a list.
		* https://en.wikipedia.org/wiki/Cycle_detection
		*/

		functionmain () {
		functiondetectCycle (head) {
		/*
		Problem Statement:
		Given head, the head of a linked list, determine if the linked list has a cycle in it.

		Note:
		* While Solving the problem in given link below, don't use main() function.
		* Just use only the code inside main() function.
		* The purpose of using main() function here is to avoid global variables.

		Link for the Problem: https://leetcode.com/problems/linked-list-cycle/
		*/
		const head = '' // Reference to head is given in the problem. So please ignore this line
		let fast = head
		let slow = head
		if (!head) { return false }

		while (fast != null && fast.next != null && slow != null) {
		let slow = head
		let fast = head.next
		while (fast && fast.next) {
		if (fast === slow) { return true }
		fast = fast.next.next
		slow = slow.next
		if (fast === slow) {
		return true
		}
		}
		return false
		}

		main()
		export { detectCycle }
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,31 @@
		import { detectCycle } from '../CycleDetection'
		import { Node } from '../SinglyLinkedList'

		describe('Detect Cycle', () => {
		it('should detect loop and return true', () => {
		// Creating list and making a loop
		const headNode = new Node(10)
		headNode.next = new Node(20)
		headNode.next.next = new Node(30)
		headNode.next.next.next = new Node(40)
		headNode.next.next.next.next = headNode
		expect(detectCycle(headNode)).toEqual(true)
		})

		it('should not detect a loop and return false', () => {
		// Case 0: When head is null, there is no loop.
		expect(detectCycle(null)).toEqual(false)
		const headNode = new Node(10)

		// Case 1: List with single node doesn't have any loop
		expect(detectCycle(headNode)).toEqual(false)

		headNode.next = new Node(20)
		headNode.next.next = new Node(30)
		headNode.next.next.next = new Node(40)
		headNode.next.next.next.next = new Node(50)

		// Case 2: List not having any loops
		expect(detectCycle(headNode)).toEqual(false)
		})
		})