algorithm: find the middle of linked-list

Data-Structures/Linked-List/MiddleOfLinkedList.js

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+/**
+ * A LinkedList based solution for finding middle node of linked list.
+ * https://afteracademy.com/blog/middle-of-the-linked-list
+ */
+class MiddleOfLL {
+ solution (head) {
+ /*
+ Problem Statement:
+ Given the head of a singly linked list, return the middle node of the linked list.
+ If there are two middle nodes, return the second middle node.
+
+ Link for the Problem: https://leetcode.com/problems/middle-of-the-linked-list/
+ */
+ let fast = head
+ let slow = head
+
+ if (head.next == null) { return head }
+
+ while (fast != null && fast.next != null) {
+ fast = fast.next.next
+ slow = slow.next
+ }
+ return slow
+ }
+}
+
+export { MiddleOfLL }

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

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+import { MiddleOfLL } from '../MiddleOfLinkedList'
+import { LinkedList } from '../SinglyLinkedList'
+
+describe('MiddleOfLinkedList', () => {
+ it('middle node Of linked list - even length ', () => {
+ const list = new LinkedList()
+ list.addFirst(1)
+ list.addLast(2)
+ list.addLast(3)
+ list.addLast(4)
+ list.addLast(5)
+ list.addLast(6)
+ list.addLast(7)
+
+ const MiddleNodeOfLinkedList = new MiddleOfLL().solution(list.headNode)
+ expect(MiddleNodeOfLinkedList.data).toEqual(4)
+ })
+
+ it('middle node of linked list - odd length ', () => {
+ const list = new LinkedList()
+ list.addFirst(10)
+ list.addLast(20)
+ list.addLast(30)
+ list.addLast(40)
+ list.addLast(50)
+ list.addLast(60)
+ list.addLast(70)
+ list.addLast(80)
+
+ const MiddleNodeOfLinkedList = new MiddleOfLL().solution(list.headNode)
+ expect(MiddleNodeOfLinkedList.data).toEqual(50)
+ })
+
+ it('middle node of linked list - length 1 ', () => {
+ const list = new LinkedList()
+ list.addFirst(100)
+
+ const MiddleNodeOfLinkedList = new MiddleOfLL().solution(list.headNode)
+ expect(MiddleNodeOfLinkedList.data).toEqual(100)
+ })
+})