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Refactor Cycledetection.js and added it's test. (TheAlgorithms#1099)
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10kartik authored Sep 15, 2022
1 parent d115214 commit cf0593f
Showing 2 changed files with 39 additions and 16 deletions.
24 changes: 8 additions & 16 deletions Data-Structures/Linked-List/CycleDetection.js
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/**
* A LinkedList based solution for Detect a Cycle in a list
* A LinkedList based solution for Detecting a Cycle in a list.
* https://en.wikipedia.org/wiki/Cycle_detection
*/

function main () {
function detectCycle (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 }
31 changes: 31 additions & 0 deletions Data-Structures/Linked-List/test/CycleDetection.test.js
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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)
})
})

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