JavaScript Program to Reverse a Linked List
A linked list is a data structure where elements are stored in nodes, and each node points to the next node in the sequence. Reversing a linked list involves changing the direction of the pointers, making the last node the new head and the head the new tail.
Below are the approaches to reverse a linked list in JavaScript:
Reversing a Linked List Using Iteration
We will use a loop to iterate through the elements and the pointer nodes of the linked list and change the next pointers of each node in such a way that their order is reversed.
Example: The below code iteratively reverses the linked list in JavaScript.
class Node {
constructor(data, next = null) {
this.data = data;
this.next = next;
}
}
class LinkedList {
constructor() {
this.head = null;
}
insertFirst(data) {
this.head = new Node(data, this.head);
}
printList() {
let current = this.head;
while (current !== null) {
console.log(current.data);
current = current.next;
}
}
reverse() {
let prev = null;
let current = this.head;
let next = null;
while (current !== null) {
next = current.next;
current.next = prev;
prev = current;
current = next;
}
this.head = prev;
}
}
const linkedList = new LinkedList();
linkedList.insertFirst(3);
linkedList.insertFirst(2);
linkedList.insertFirst(1);
console.log("Original Linked List:");
linkedList.printList();
linkedList.reverse();
console.log("\nReversed Linked List:");
linkedList.printList();
Output
Original Linked List: 1 2 3 Reversed Linked List: 3 2 1
Time Complexity: O(N)
Space Complexity: O(1)
Reversing a Linked List Using Recursion
Recursion is a process in which a function calls itself directly or indirectly. We are going to reverse the linked list by iterating through its elements using recursion and change their node values.
Example: The below code is the implementation of the recursive approach to reverse the linked list in JavaScript.
class Node {
constructor(data, next = null) {
this.data = data;
this.next = next;
}
}
class LinkedList {
constructor() {
this.head = null;
}
insertFirst(data) {
this.head = new Node(data, this.head);
}
reverseRecursiveUtil(current, prev) {
if (current === null) {
this.head = prev;
return;
}
const next = current.next;
current.next = prev;
this.reverseRecursiveUtil(next, current);
}
reverseRecursive() {
this.reverseRecursiveUtil(this.head, null);
}
printList() {
let current = this.head;
while (current !== null) {
console.log(current.data);
current = current.next;
}
}
}
const linkedList = new LinkedList();
linkedList.insertFirst(3);
linkedList.insertFirst(2);
linkedList.insertFirst(1);
console.log("Original Linked List:");
linkedList.printList();
linkedList.reverseRecursive();
console.log("\nReversed Linked List:");
linkedList.printList();
Output
Original Linked List: 1 2 3 Reversed Linked List: 3 2 1
Time Complexity: O(N)
Space Complexity: O(N)
