From c5101e3e2b6f05240b7da3182e3739585dd7b073 Mon Sep 17 00:00:00 2001
From: Khushi Shukla <tusharika.shukla05@gmail.com>
Date: Sun, 30 Oct 2022 14:46:56 +0530
Subject: [PATCH] chore: add reverse to singly linked list (#1241)

* Fix: Reverse Singly Linked List

* Added reverse in SinglyLinkedList

* Added reverse in SinglyLinkedList

* Changes made
---
 .../Linked-List/ReverseSinglyLinkedList.js       | 16 ++++++++++++++++
 Data-Structures/Linked-List/SinglyLinkedList.js  | 14 ++++++++++++++
 .../test/ReverseSinglyLinkedList.test.js         | 14 ++++++++++++++
 .../Linked-List/test/SinglyLinkedList.test.js    |  6 ++++++
 4 files changed, 50 insertions(+)
 create mode 100644 Data-Structures/Linked-List/ReverseSinglyLinkedList.js
 create mode 100644 Data-Structures/Linked-List/test/ReverseSinglyLinkedList.test.js

diff --git a/Data-Structures/Linked-List/ReverseSinglyLinkedList.js b/Data-Structures/Linked-List/ReverseSinglyLinkedList.js
new file mode 100644
index 000000000..db4e7ef6d
--- /dev/null
+++ b/Data-Structures/Linked-List/ReverseSinglyLinkedList.js
@@ -0,0 +1,16 @@
+/** A LinkedList based solution to reverse a number
+Problem Statement: Given a number such that each of its digit is stored in a singly linked list. Reverse the linked list and return the head of the linked list Link for the Problem: https://leetcode.com/problems/reverse-linked-list/ */
+class ReverseSinglyLinkedList {
+  solution (head) {
+    let prev = null
+    let next = null
+    while (head) {
+      next = head.next
+      head.next = prev
+      prev = head
+      head = next
+    }
+    return prev
+  };
+}
+export { ReverseSinglyLinkedList }
diff --git a/Data-Structures/Linked-List/SinglyLinkedList.js b/Data-Structures/Linked-List/SinglyLinkedList.js
index d55e0b14b..605ede401 100644
--- a/Data-Structures/Linked-List/SinglyLinkedList.js
+++ b/Data-Structures/Linked-List/SinglyLinkedList.js
@@ -274,6 +274,20 @@ class LinkedList {
   log () {
     console.log(JSON.stringify(this.headNode, null, 2))
   }
+
+  // Method to reverse the LinkedList
+  reverse () {
+    let head = this.headNode
+    let prev = null
+    let next = null
+    while (head) {
+      next = head.next
+      head.next = prev
+      prev = head
+      head = next
+    }
+    this.headNode = prev
+  };
 }
 
 export { Node, LinkedList }
diff --git a/Data-Structures/Linked-List/test/ReverseSinglyLinkedList.test.js b/Data-Structures/Linked-List/test/ReverseSinglyLinkedList.test.js
new file mode 100644
index 000000000..847026db8
--- /dev/null
+++ b/Data-Structures/Linked-List/test/ReverseSinglyLinkedList.test.js
@@ -0,0 +1,14 @@
+import { ReverseSinglyLinkedList } from '../ReverseSinglyLinkedList'
+import { Node } from '../SinglyLinkedList'
+describe('ReverseSinglyLinkedList', () => {
+  it('Reverse a Number Represented as Linked List', () => {
+    const headNode = new Node(3)
+    headNode.next = new Node(4)
+    headNode.next.next = new Node(1)
+    const expected = new Node(1)
+    expected.next = new Node(4)
+    expected.next.next = new Node(3)
+    const reverseSinglyLinkedList = new ReverseSinglyLinkedList()
+    expect(reverseSinglyLinkedList.solution(headNode)).toEqual(expected)
+  })
+})
diff --git a/Data-Structures/Linked-List/test/SinglyLinkedList.test.js b/Data-Structures/Linked-List/test/SinglyLinkedList.test.js
index 764cac7aa..a04d06ba1 100644
--- a/Data-Structures/Linked-List/test/SinglyLinkedList.test.js
+++ b/Data-Structures/Linked-List/test/SinglyLinkedList.test.js
@@ -247,4 +247,10 @@ describe('SinglyLinkedList', () => {
     headNode.rotateListRight(5)
     expect(headNode.get()).toEqual([20, 30, 40, 50, 10])
   })
+
+  it('Reverse a Linked List', () => {
+    const list = new LinkedList([4, 3, 1])
+    list.reverse()
+    expect(list.get()).toEqual([1, 3, 4])
+  })
 })