Java Program for Reverse a linked list
Last Updated :
17 Jun, 2022
Given a pointer to the head node of a linked list, the task is to reverse the linked list. We need to reverse the list by changing links between nodes. Examples:
Input: Head of following linked list
1->2->3->4->NULL
Output: Linked list should be changed to,
4->3->2->1->NULL
Input: Head of following linked list
1->2->3->4->5->NULL
Output: Linked list should be changed to,
5->4->3->2->1->NULL
Input: NULL
Output: NULL
Input: 1->NULL
Output: 1->NULL
Iterative Method:
Java
// Java program for reversing the linked list
class LinkedList {
static Node head;
static class Node {
int data;
Node next;
Node(int d) {
data = d;
next = null;
}
}
/* Function to reverse the linked list */
Node reverse(Node node) {
Node prev = null;
Node current = node;
Node next = null;
while (current != null) {
next = current.next;
current.next = prev;
prev = current;
current = next;
}
node = prev;
return node;
}
// prints content of double linked list
void printList(Node node) {
while (node != null) {
System.out.print(node.data + " ");
node = node.next;
}
}
public static void main(String[] args) {
LinkedList list = new LinkedList();
list.head = new Node(85);
list.head.next = new Node(15);
list.head.next.next = new Node(4);
list.head.next.next.next = new Node(20);
System.out.println("Given Linked list");
list.printList(head);
head = list.reverse(head);
System.out.println("");
System.out.println("Reversed linked list ");
list.printList(head);
}
}
// This code has been contributed by Mayank Jaiswal
OutputGiven Linked list
85 15 4 20
Reversed linked list
20 4 15 85
Time Complexity: O(N), where N is the length of the given linked list
Auxiliary Space: O(1)
A Simpler and Tail Recursive Method:
Java
// Java program for reversing the Linked list
class LinkedList {
static Node head;
static class Node {
int data;
Node next;
Node(int d) {
data = d;
next = null;
}
}
// A simple and tail recursive function to reverse
// a linked list. prev is passed as NULL initially.
Node reverseUtil(Node curr, Node prev) {
/* If last node mark it head*/
if (curr.next == null) {
head = curr;
/* Update next to prev node */
curr.next = prev;
return null;
}
/* Save curr->next node for recursive call */
Node next1 = curr.next;
/* and update next ..*/
curr.next = prev;
reverseUtil(next1, curr);
return head;
}
// prints content of double linked list
void printList(Node node) {
while (node != null) {
System.out.print(node.data + " ");
node = node.next;
}
}
public static void main(String[] args) {
LinkedList list = new LinkedList();
list.head = new Node(1);
list.head.next = new Node(2);
list.head.next.next = new Node(3);
list.head.next.next.next = new Node(4);
list.head.next.next.next.next = new Node(5);
list.head.next.next.next.next.next = new Node(6);
list.head.next.next.next.next.next.next = new Node(7);
list.head.next.next.next.next.next.next.next = new Node(8);
System.out.println("Original Linked list ");
list.printList(head);
Node res = list.reverseUtil(head, null);
System.out.println("");
System.out.println("");
System.out.println("Reversed linked list ");
list.printList(res);
}
}
// This code has been contributed by Mayank Jaiswal
OutputOriginal Linked list
1 2 3 4 5 6 7 8
Reversed linked list
8 7 6 5 4 3 2 1
Time Complexity: O(N), where N is the length of the given linked list
Auxiliary Space: O(1)
Please refer complete article on Reverse a linked list for more details!
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