Reverse a linked list - GeeksforGeeks

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

Initialize three pointers prev as NULL, curr as head and next as NULL.

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++

// 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;
}

C

// 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();
}

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;
        }
    }
 
    // 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

Python

# 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)

C#

// 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

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++

// 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;
}

Java

// 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

Python3

"""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

C#

// 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

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++

// 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;
}

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 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

Python

# 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)

C#

// 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

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++

// 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;
}

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

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