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Refactor Cycledetection.js and added it's test. (TheAlgorithms#1099)
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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 | ||
*/ | ||
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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 } | ||
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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 | ||
} | ||
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main() | ||
export { detectCycle } |
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import { detectCycle } from '../CycleDetection' | ||
import { Node } from '../SinglyLinkedList' | ||
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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) | ||
}) | ||
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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) | ||
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// Case 1: List with single node doesn't have any loop | ||
expect(detectCycle(headNode)).toEqual(false) | ||
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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) | ||
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// Case 2: List not having any loops | ||
expect(detectCycle(headNode)).toEqual(false) | ||
}) | ||
}) |