Reverse a linked list

 

Given 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 the 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 

  1. Initialize three pointers prev as NULL, curr as head and next as NULL.
  2. Iterate through the linked list. In loop, do following. 
    // Before changing next of current, 
    // store next node 
    next = curr->next
    // Now change next of current 
    // This is where actual reversing happens 
    curr->next = prev 
    // Move prev and curr one step forward 
    prev = curr 
    curr = next

Below is the implementation of the above approach: 

C++

filter_none

edit
close

play_arrow

link
brightness_4
code

// Iterative C++ program to reverse
// a linked list
#include <iostream>
using namespace std;
 
/* Link list node */
struct Node {
    int data;
    struct Node* next;
    Node(int data)
    {
        this->data = data;
        next = NULL;
    }
};
 
struct LinkedList {
    Node* head;
    LinkedList() { head = NULL; }
 
    /* Function to reverse the linked list */
    void reverse()
    {
        // Initialize current, previous and
        // next pointers
        Node* current = head;
        Node *prev = NULL, *next = NULL;
 
        while (current != NULL) {
            // Store next
            next = current->next;
 
            // Reverse current node's pointer
            current->next = prev;
 
            // Move pointers one position ahead.
            prev = current;
            current = next;
        }
        head = prev;
    }
 
    /* Function to print linked list */
    void print()
    {
        struct Node* temp = head;
        while (temp != NULL) {
            cout << temp->data << " ";
            temp = temp->next;
        }
    }
 
    void push(int data)
    {
        Node* temp = new Node(data);
        temp->next = head;
        head = temp;
    }
};
 
/* Driver code*/
int main()
{
    /* Start with the empty list */
    LinkedList ll;
    ll.push(20);
    ll.push(4);
    ll.push(15);
    ll.push(85);
 
    cout << "Given linked list\n";
    ll.print();
 
    ll.reverse();
 
    cout << "\nReversed Linked list \n";
    ll.print();
    return 0;
}

chevron_right


C

filter_none

edit
close

play_arrow

link
brightness_4
code

// Iterative C program to reverse a linked list
#include <stdio.h>
#include <stdlib.h>
 
/* Link list node */
struct Node {
    int data;
    struct Node* next;
};
 
/* Function to reverse the linked list */
static void reverse(struct Node** head_ref)
{
    struct Node* prev = NULL;
    struct Node* current = *head_ref;
    struct Node* next = NULL;
    while (current != NULL) {
        // Store next
        next = current->next;
 
        // Reverse current node's pointer
        current->next = prev;
 
        // Move pointers one position ahead.
        prev = current;
        current = next;
    }
    *head_ref = prev;
}
 
/* Function to push a node */
void push(struct Node** head_ref, int new_data)
{
    struct Node* new_node
        = (struct Node*)malloc(sizeof(struct Node));
    new_node->data = new_data;
    new_node->next = (*head_ref);
    (*head_ref) = new_node;
}
 
/* Function to print linked list */
void printList(struct Node* head)
{
    struct Node* temp = head;
    while (temp != NULL) {
        printf("%d  ", temp->data);
        temp = temp->next;
    }
}
 
/* Driver code*/
int main()
{
    /* Start with the empty list */
    struct Node* head = NULL;
 
    push(&head, 20);
    push(&head, 4);
    push(&head, 15);
    push(&head, 85);
 
    printf("Given linked list\n");
    printList(head);
    reverse(&head);
    printf("\nReversed Linked list \n");
    printList(head);
    getchar();
}

chevron_right


Java

filter_none

edit
close

play_arrow

link
brightness_4
code

// 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;
        }
    }
 
    // Driver Code
    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

chevron_right


Python

filter_none

edit
close

play_arrow

link
brightness_4
code

# 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
 
 
class LinkedList:
 
    # Function to initialize head
    def __init__(self):
        self.head = None
 
    # Function to reverse the linked list
    def reverse(self):
        prev = None
        current = self.head
        while(current is not None):
            next = current.next
            current.next = prev
            prev = current
            current = next
        self.head = prev
 
    # Function to insert a new node at the beginning
    def push(self, new_data):
        new_node = Node(new_data)
        new_node.next = self.head
        self.head = new_node
 
    # Utility function to print the linked LinkedList
    def printList(self):
        temp = self.head
        while(temp):
            print temp.data,
            temp = temp.next
 
 
# Driver code
llist = LinkedList()
llist.push(20)
llist.push(4)
llist.push(15)
llist.push(85)
 
print "Given Linked List"
llist.printList()
llist.reverse()
print "\nReversed Linked List"
llist.printList()
 
# This code is contributed by Nikhil Kumar Singh(nickzuck_007)

chevron_right


C#

filter_none

edit
close

play_arrow

link
brightness_4
code

// C# program for reversing the linked list
using System;
 
class GFG {
   
    // Driver Code
    static void Main(string[] args)
    {
        LinkedList list = new LinkedList();
        list.AddNode(new LinkedList.Node(85));
        list.AddNode(new LinkedList.Node(15));
        list.AddNode(new LinkedList.Node(4));
        list.AddNode(new LinkedList.Node(20));
 
        // List before reversal
        Console.WriteLine("Given linked list:");
        list.PrintList();
 
        // Reverse the list
        list.ReverseList();
 
        // List after reversal
        Console.WriteLine("Reversed linked list:");
        list.PrintList();
    }
}
 
class LinkedList {
    Node head;
 
    public class Node {
        public int data;
        public Node next;
 
        public Node(int d)
        {
            data = d;
            next = null;
        }
    }
 
    // function to add a new node at
    // the end of the list
    public void AddNode(Node node)
    {
        if (head == null)
            head = node;
        else {
            Node temp = head;
            while (temp.next != null) {
                temp = temp.next;
            }
            temp.next = node;
        }
    }
 
    // function to reverse the list
    public void ReverseList()
    {
        Node prev = null, current = head, next = null;
        while (current != null) {
            next = current.next;
            current.next = prev;
            prev = current;
            current = next;
        }
        head = prev;
    }
 
    // function to print the list data
    public void PrintList()
    {
        Node current = head;
        while (current != null) {
            Console.Write(current.data + " ");
            current = current.next;
        }
        Console.WriteLine();
    }
}
 
// This code is contributed by Mayank Sharma

chevron_right


Output: 

Given linked list
85 15 4 20 
Reversed Linked list 
20 4 15 85 

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

Recursive Method: 

   1) Divide the list in two parts - first node and 
      rest of the linked list.
   2) Call reverse for the rest of the linked list.
   3) Link rest to first.
   4) Fix head pointer 

Linked List Rverse



C++

filter_none

edit
close

play_arrow

link
brightness_4
code

// Recursive C++ program to reverse
// a linked list
#include <iostream>
using namespace std;
 
/* Link list node */
struct Node {
    int data;
    struct Node* next;
    Node(int data)
    {
        this->data = data;
        next = NULL;
    }
};
 
struct LinkedList {
    Node* head;
    LinkedList()
    {
        head = NULL;
    }
 
    Node* reverse(Node* head)
    {
        if (head == NULL || head->next == NULL)
            return head;
 
        /* reverse the rest list and put
          the first element at the end */
        Node* rest = reverse(head->next);
        head->next->next = head;
 
        /* tricky step -- see the diagram */
        head->next = NULL;
 
        /* fix the head pointer */
        return rest;
    }
 
    /* Function to print linked list */
    void print()
    {
        struct Node* temp = head;
        while (temp != NULL) {
            cout << temp->data << " ";
            temp = temp->next;
        }
    }
 
    void push(int data)
    {
        Node* temp = new Node(data);
        temp->next = head;
        head = temp;
    }
};
 
/* Driver program to test above function*/
int main()
{
    /* Start with the empty list */
    LinkedList ll;
    ll.push(20);
    ll.push(4);
    ll.push(15);
    ll.push(85);
 
    cout << "Given linked list\n";
    ll.print();
 
    ll.head = ll.reverse(ll.head);
 
    cout << "\nReversed Linked list \n";
    ll.print();
    return 0;
}

chevron_right


Java

filter_none

edit
close

play_arrow

link
brightness_4
code

// Recursive Java program to reverse
// a linked list
class recursion {
    static Node head; // head of list
     
    static class Node {
        int data;
        Node next;
        Node(int d)
        {
            data = d;
            next = null;
        }
    }
 
    static Node reverse(Node head)
    {
        if (head == null || head.next == null)
            return head;
 
        /* reverse the rest list and put
        the first element at the end */
        Node rest = reverse(head.next);
        head.next.next = head;
 
        /* tricky step -- see the diagram */
        head.next = null;
 
        /* fix the head pointer */
        return rest;
    }
 
    /* Function to print linked list */
    static void print()
    {
        Node temp = head;
        while (temp != null) {
            System.out.print(temp.data + " ");
            temp = temp.next;
        }
        System.out.println();
    }
 
    static void push(int data)
    {
        Node temp = new Node(data);
        temp.next = head;
        head = temp;
    }
  
 
/* Driver program to test above function*/
public static void main(String args[])
{
    /* Start with the empty list */
      
    push(20);
    push(4);
    push(15);
    push(85);
 
    System.out.println("Given linked list");
    print();
 
    head = reverse(head);
 
    System.out.println("Reversed Linked list");
    print();
}
}
 
// This code is contributed by Prakhar Agarwal

chevron_right


Python3

filter_none

edit
close

play_arrow

link
brightness_4
code

"""Python3 program to reverse linked list
using recursive method"""
 
# Linked List Node
class Node:
    def __init__(self, data):
        self.data = data
        self.next = None
 
# Create and Handle list operations
class LinkedList:
    def __init__(self):
        self.head = None # Head of list
 
    # Method to reverse the list
    def reverse(self, head):
 
        # If head is empty or has reached the list end
        if head is None or head.next is None:
            return head
 
        # Reverse the rest list
        rest = self.reverse(head.next)
 
        # Put first element at the end
        head.next.next = head
        head.next = None
 
        # Fix the header pointer
        return rest
 
    # Returns the linked list in display format
    def __str__(self):
        linkedListStr = ""
        temp = self.head
        while temp:
            linkedListStr = (linkedListStr +
                            str(temp.data) + " ")
            temp = temp.next
        return linkedListStr
 
    # Pushes new data to the head of the list
    def push(self, data):
        temp = Node(data)
        temp.next = self.head
        self.head = temp
 
# Driver code
linkedList = LinkedList()
linkedList.push(20)
linkedList.push(4)
linkedList.push(15)
linkedList.push(85)
 
print("Given linked list")
print(linkedList)
 
linkedList.head = linkedList.reverse(linkedList.head)
 
print("Reversed linked list")
print(linkedList)
 
# This code is contributed by Debidutta Rath

chevron_right


C#

filter_none

edit
close

play_arrow

link
brightness_4
code

// Recursive C# program to
// reverse a linked list
using System;
class recursion{
     
// Head of list
static Node head;
 
public class Node
{
  public int data;
  public Node next;
  public Node(int d)
  {
    data = d;
    next = null;
  }
}
 
static Node reverse(Node head)
{
  if (head == null ||
      head.next == null)
    return head;
 
  // Reverse the rest list and put 
  // the first element at the end
  Node rest = reverse(head.next);
  head.next.next = head;
 
  // Tricky step --
  // see the diagram
  head.next = null;
 
  // Fix the head pointer
  return rest;
}
 
// Function to print
// linked list
static void print()
{
  Node temp = head;
  while (temp != null)
  {
    Console.Write(temp.data + " ");
    temp = temp.next;
  }
  Console.WriteLine();
}
 
static void push(int data)
{
  Node temp = new Node(data);
  temp.next = head;
  head = temp;
}
 
// Driver code
public static void Main(String []args)
{
  // Start with the
  // empty list
  push(20);
  push(4);
  push(15);
  push(85);
 
  Console.WriteLine("Given linked list");
  print();
  head = reverse(head);
  Console.WriteLine("Reversed Linked list");
  print();
}
}
 
// This code is contributed by gauravrajput1

chevron_right


Output: 

Given linked list
85 15 4 20 
Reversed Linked list
20 4 15 85 

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

A Simpler and Tail Recursive Method 

Below is the implementation of this method.  

C++

filter_none

edit
close

play_arrow

link
brightness_4
code

// A simple and tail recursive C++ program to reverse
// a linked list
#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
void reverse(Node** head)
{
    if (!head)
        return;
    reverseUtil(*head, NULL, head);
}
 
// 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) {
        *head = curr;
 
        /* 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;
 
    reverseUtil(next, curr, head);
}
 
// 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
void printlist(Node* head)
{
    while (head != NULL) {
        cout << head->data << " ";
        head = head->next;
    }
    cout << endl;
}
 
// Driver code
int main()
{
    Node* head1 = newNode(1);
    head1->next = newNode(2);
    head1->next->next = newNode(3);
    head1->next->next->next = newNode(4);
    head1->next->next->next->next = newNode(5);
    head1->next->next->next->next->next = newNode(6);
    head1->next->next->next->next->next->next = newNode(7);
    head1->next->next->next->next->next->next->next
        = newNode(8);
    cout << "Given linked list\n";
    printlist(head1);
    reverse(&head1);
    cout << "\nReversed linked list\n";
    printlist(head1);
    return 0;
}

chevron_right


Java

filter_none

edit
close

play_arrow

link
brightness_4
code

// 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 head is initially null OR list is empty*/
        if (head == null)
            return head;
        /* If last node mark it head*/
        if (curr.next == null) {
            head = curr;
 
            /* Update next to prev node */
            curr.next = prev;
 
            return head;
        }
 
        /* 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;
        }
    }
 
    // Driver Code
    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

chevron_right


Python

filter_none

edit
close

play_arrow

link
brightness_4
code

# Simple and tail recursive Python program to
# reverse a linked list
 
# Node class
 
 
class Node:
 
    # Constructor to initialize the node object
    def __init__(self, data):
        self.data = data
        self.next = None
 
 
class LinkedList:
 
    # Function to initialize head
    def __init__(self):
        self.head = None
 
    def reverseUtil(self, curr, prev):
 
        # If last node mark it head
        if curr.next is None:
            self.head = curr
 
            # 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):
        if self.head is None:
            return
        self.reverseUtil(self.head, None)
 
    # Function to insert a new node at the beginning
 
    def push(self, new_data):
        new_node = Node(new_data)
        new_node.next = self.head
        self.head = new_node
 
    # Utility function to print the linked LinkedList
    def printList(self):
        temp = self.head
        while(temp):
            print temp.data,
            temp = temp.next
 
 
# Driver code
llist = LinkedList()
llist.push(8)
llist.push(7)
llist.push(6)
llist.push(5)
llist.push(4)
llist.push(3)
llist.push(2)
llist.push(1)
 
print "Given linked list"
llist.printList()
 
llist.reverse()
 
print "\nReverse linked list"
llist.printList()
 
# This code is contributed by Nikhil Kumar Singh(nickzuck_007)

chevron_right


C#

filter_none

edit
close

play_arrow

link
brightness_4
code

// C# program for reversing the Linked list
using System;
 
public class LinkedList {
    Node head;
    public class Node {
 
        public int data;
        public Node next;
 
        public 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 head;
        }
 
        /* 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) {
            Console.Write(node.data + " ");
            node = node.next;
        }
    }
 
    // Driver code
    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);
 
        Console.WriteLine("Original Linked list ");
        list.printList(list.head);
        Node res = list.reverseUtil(list.head, null);
        Console.WriteLine("");
        Console.WriteLine("");
        Console.WriteLine("Reversed linked list ");
        list.printList(res);
    }
}
 
// This code contributed by Rajput-Ji

chevron_right


Output

Given linked list
1 2 3 4 5 6 7 8 

Reversed linked list
8 7 6 5 4 3 2 1 

Using Stack:

  • Store the nodes(values and address) in the stack until all the values are entered.
  • Once all entries are done, Update the Head pointer to the last location(i.e the last value).
  • Start popping the nodes(value and address) and store them in the same order until the stack is empty.
  • Update the next pointer of last Node in the stack by NULL.

Below is the implementation of the above approach:

C++

filter_none

edit
close

play_arrow

link
brightness_4
code

// C++ program for above approach
#include <bits/stdc++.h>
#include <iostream>
using namespace std;
 
// Create a class Node to enter
// values and address in the list
class Node
{
public:
    int data;
    Node* next;
};
 
// Function to reverse the
// linked list
void reverseLL(Node** head)
{  
     
    // Create a stack "s"
    // of Node type
    stack<Node*> s;
    Node* temp = *head;
    while (temp->next != NULL)
    {
         
        // Push all the nodes
        // in to stack
        s.push(temp);
        temp = temp->next;
    }
    *head = temp;
   
    while (!s.empty())
    {
         
        // Store the top value of
        // stack in list
        temp->next = s.top();
       
        // Pop the value from stack
        s.pop();
       
        // update the next pointer in the
        // in the list
        temp = temp->next;
    }
    temp->next = NULL;
}
 
// Function to Display
// the elements in List
void printlist(Node* temp)
{
    while (temp != NULL)
    {
        cout << temp->data << " ";
        temp = temp->next;
    }
}
 
// Program to insert back of the
// linked list
void insert_back(Node** head, int value)
{
 
    // we have used insertion at back method
    // to enter values in the list.(eg:
    // head->1->2->3->4->Null)
    Node* temp = new Node();
    temp->data = value;
    temp->next = NULL;
     
    // If *head equals to NULL
    if (*head == NULL)
    {
      *head = temp;
      return;
    }
    else
    {
      Node* last_node = *head;
      while (last_node->next != NULL)
      {
        last_node = last_node->next;
      }
      last_node->next = temp;
      return;
    }
}
 
// Driver Code
int main()
{
    Node* head = NULL;
 
    insert_back(&head, 1);
    insert_back(&head, 2);
    insert_back(&head, 3);
    insert_back(&head, 4);
    cout << "Given linked list\n";
    printlist(head);
    reverseLL(&head);
    cout << "\nReversed linked list\n";
    printlist(head);
    return 0;
}

chevron_right


Output

Given linked list
1 2 3 4 
Reversed linked list
4 3 2 1 

Thanks to Gaurav Ahirwar for suggesting this solution. 
Recursively Reversing a linked list (A simple implementation) 
Iteratively Reverse a linked list using only 2 pointers (An Interesting Method)

References: 
http://cslibrary.stanford.edu/105/LinkedListProblems.pdf

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.




My Personal Notes arrow_drop_up