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

Data-Structures/Linked-List/test/CycleDetection.test.js

@@ -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)
+  })
+})