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Refactor Cycledetection.js and added it's test. (TheAlgorithms#1099)

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Lines changed: 8 additions & 16 deletions

Original file line number	Diff line number	Diff line change
`@@ -1,32 +1,24 @@`
`1`	`1`	`/**`
`2`		`- * A LinkedList based solution for Detect a Cycle in a list`
	`2`	`+ * A LinkedList based solution for Detecting a Cycle in a list.`
`3`	`3`	`* https://en.wikipedia.org/wiki/Cycle_detection`
`4`	`4`	`*/`
`5`	`5`
`6`		`-function main() {`
	`6`	`+function detectCycle(head) {`
`7`	`7`	`/*`
`8`	`8`	`Problem Statement:`
`9`	`9`	`Given head, the head of a linked list, determine if the linked list has a cycle in it.`
`10`		`-`
`11`		`- Note:`
`12`		`- * While Solving the problem in given link below, don't use main() function.`
`13`		`- * Just use only the code inside main() function.`
`14`		`- * The purpose of using main() function here is to avoid global variables.`
`15`		`-`
`16`	`10`	`Link for the Problem: https://leetcode.com/problems/linked-list-cycle/`
`17`	`11`	`*/`
`18`		`- const head = '' // Reference to head is given in the problem. So please ignore this line`
`19`		`- let fast = head`
`20`		`- let slow = head`
	`12`	`+ if (!head) { return false }`
`21`	`13`
`22`		`- while (fast != null && fast.next != null && slow != null) {`
	`14`	`+ let slow = head`
	`15`	`+ let fast = head.next`
	`16`	`+ while (fast && fast.next) {`
	`17`	`+ if (fast === slow) { return true }`
`23`	`18`	`fast = fast.next.next`
`24`	`19`	`slow = slow.next`
`25`		`- if (fast === slow) {`
`26`		`- return true`
`27`		`- }`
`28`	`20`	`}`
`29`	`21`	`return false`
`30`	`22`	`}`
`31`	`23`
`32`		`-main()`
	`24`	`+export{detectCycle}`

Lines changed: 31 additions & 0 deletions

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,31 @@`
	`1`	`+import { detectCycle } from '../CycleDetection'`
	`2`	`+import { Node } from '../SinglyLinkedList'`
	`3`	`+`
	`4`	`+describe('Detect Cycle', () => {`
	`5`	`+ it('should detect loop and return true', () => {`
	`6`	`+ // Creating list and making a loop`
	`7`	`+ const headNode = new Node(10)`
	`8`	`+ headNode.next = new Node(20)`
	`9`	`+ headNode.next.next = new Node(30)`
	`10`	`+ headNode.next.next.next = new Node(40)`
	`11`	`+ headNode.next.next.next.next = headNode`
	`12`	`+ expect(detectCycle(headNode)).toEqual(true)`
	`13`	`+ })`
	`14`	`+`
	`15`	`+ it('should not detect a loop and return false', () => {`
	`16`	`+ // Case 0: When head is null, there is no loop.`
	`17`	`+ expect(detectCycle(null)).toEqual(false)`
	`18`	`+ const headNode = new Node(10)`
	`19`	`+`
	`20`	`+ // Case 1: List with single node doesn't have any loop`
	`21`	`+ expect(detectCycle(headNode)).toEqual(false)`
	`22`	`+`
	`23`	`+ headNode.next = new Node(20)`
	`24`	`+ headNode.next.next = new Node(30)`
	`25`	`+ headNode.next.next.next = new Node(40)`
	`26`	`+ headNode.next.next.next.next = new Node(50)`
	`27`	`+`
	`28`	`+ // Case 2: List not having any loops`
	`29`	`+ expect(detectCycle(headNode)).toEqual(false)`
	`30`	`+ })`
	`31`	`+})`

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