Courses βeta
Data Structures

Examples:

Input : Head of following linked list

1->2->3->4->NULL

Output : Linked list should be changed to,

4->3->2->1->NULL

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 Iterate trough the linked list. In the loop, change next to prev, prev to current and current to next.

Implementation of Iterative Method

#include<stdio.h>
#include<stdlib.h>

struct node
{
int data;
struct node* next;
};

/* Function to reverse the linked list */
{
struct node* prev = NULL;
struct node* next;
while (current != NULL)
{
next = current->next;
current->next = prev;
prev = current;
current = next;
}
}

/* Function to push a node */
void push(struct node** head_ref, int new_data)
{
/* allocate node */
struct node* new_node =
(struct node*) malloc(sizeof(struct node));

/* put in the data */
new_node->data = new_data;

/* link the old list off the new node */

/* move the head to point to the new node */
}

/* Function to print linked list */
{
while(temp != NULL)
{
printf("%d ", temp->data);
temp = temp->next;
}
}

/* Driver program to test above function*/
int main()
{

getchar();
}


// Java program for reversing the linked list

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) {

System.out.println("");
}
}


# Python program to reverse a linked list
# Time Complexity : O(n)
# Space Complexity : O(1)

# Node class
class Node:

# Constructor to initialize the node object
def __init__(self, data):
self.data = data
self.next = None

def __init__(self):

# Function to reverse the linked list
def reverse(self):
prev = None
while(current is not None):
next = current.next
current.next = prev
prev = current
current = next

# Function to insert a new node at the beginning
def push(self, new_data):
new_node = Node(new_data)

def printList(self):
while(temp):
print temp.data,
temp = temp.next

# Driver program to test above functions
llist.push(20)
llist.push(4)
llist.push(15)
llist.push(85)

llist.printList()
llist.reverse()
llist.printList()


Output:

85 15 4 20
20 4 15 85


Time Complexity: O(n) Space Complexity: O(1)

Recursive Method:

  1) Divide the list into two parts - first node and rest of the linked list.
2) Call reverse for the rest of the linked list.


void recursiveReverse(struct node** head_ref)
{
struct node* first;
struct node* rest;

/* empty list */
return;

/* suppose first = {1, 2, 3}, rest = {2, 3} */
rest = first->next;

/* List has only one node */
if (rest == NULL)
return;

/* reverse the rest list and put the first element at the end */
recursiveReverse(&rest);
first->next->next = first;

/* tricky step -- see the diagram */
first->next = NULL;

/* fix the head pointer */
}


Time Complexity: O(n) Space Complexity: O(1)

A Simpler and Tail Recursive Method Below is C++ implementation of this method.

// A simple and tail recursive C++ program to reverse
#include<bits/stdc++.h>
using namespace std;

struct node
{
int data;
struct node *next;
};

void reverseUtil(node *curr, node *prev, node **head);

// This function mainly calls reverseUtil()
// with prev as NULL
{
return;
}

// A simple and tail recursive function to reverse
// a linked list. prev is passed as NULL initially.
void reverseUtil(node *curr, node *prev, node **head)
{
/* If last node mark it head*/
if (!curr->next)
{

/* Update next to prev node */
curr->next = prev;
return;
}

/* Save curr->next node for recursive call */
node *next = curr->next;

/* and update next ..*/
curr->next = prev;

}

// A utility function to create a new node
node *newNode(int key)
{
node *temp = new node;
temp->data = key;
temp->next = NULL;
return temp;
}

// A utility function to print a linked list
{
{
cout << head->data << " ";
}
cout << endl;
}

// Driver program to test above functions
int main()
{
return 0;
}


// Java program for reversing the Linked list

cpp
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) {

/* 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);
}

// 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) {

System.out.println("");
System.out.println("");
list.printList(res);
}
}


# Simple and tail recursive Python program to

# Node class
class Node:

# Constructor to initialize the node object
def __init__(self, data):
self.data = data
self.next = None

def __init__(self):

def reverseUtil(self, curr, prev):

# If last node mark it head
if curr.next is None :

# Update next to prev node
curr.next = prev
return

# Save curr.next node for recursive call
next = curr.next

# And update next
curr.next = prev

self.reverseUtil(next, curr)

# This function mainly calls reverseUtil()
# with previous as None
def reverse(self):
return

# Function to insert a new node at the beginning
def push(self, new_data):
new_node = Node(new_data)

def printList(self):
while(temp):
print temp.data,
temp = temp.next

# Driver program
llist.push(8)
llist.push(7)
llist.push(6)
llist.push(5)
llist.push(4)
llist.push(2)
llist.push(2)
llist.push(1)

llist.printList()

llist.reverse()

llist.printList()


Output:

Given linked list
1 2 2 4 5 6 7 8