Print Reverse a linked list using Stack

Given a linked list, print the reverse of it without modifying the list.

Examples: 

Input : 1 2 3 4 5 6
Output : 6 5 4 3 2 1

Input : 12 23 34 45 56 67 78
Output : 78 67 56 45 34 23 12

Below are different solutions that are now allowed here as we cannot use extra space and modify the list.

1. Recursive solution to print reverse a linked list. Requires extra space.
2. Reverse linked list and then print. This requires modifications to the original list.
3. A O(n²) solution to print reverse of linked list that first count nodes and then prints k-th node from the end.

In this post, the efficient stack-based solution is discussed. 

1. First, insert all the elements in the stack
2. Print stack till stack is not empty

Note: Instead of inserting data from each node into the stack, insert the node’s address onto the stack. This is because the size of the node’s data will be generally more than the size of the node’s address. Thus, the stack would end up requiring more memory if it directly stored the data elements. Also, we cannot insert the node’s data onto the stack if each node contained more than one data member. Hence, a simpler and efficient solution would be to simply insert the node’s address.

Below is the implementation of the above idea:

C++

// C/C++ program to print reverse of linked list
// using stack.
#include <bits/stdc++.h>
using namespace std;

// Link list node
struct Node {
    int data;
    struct Node* next;
};

// Given a reference (pointer to pointer) to the head
// of a list and an int,
// push a new node on the front of the list.
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;
}

// Counts no. of nodes in linked list
int getCount(struct Node* head)
{
    int count = 0; // Initialize count
    struct Node* current = head; // Initialize current
    while (current != NULL) {
        count++;
        current = current->next;
    }
    return count;
}

// Takes head pointer of the linked list and index
// as arguments and return data at index
int getNth(struct Node* head, int n)
{
    struct Node* curr = head;
    for (int i = 0; i < n - 1 && curr != NULL; i++)
        curr = curr->next;
    return curr->data;
}

void printReverse(Node* head)
{
    // store Node addresses in stack
    stack<Node*> stk;
    Node* ptr = head;
    while (ptr != NULL) {
        stk.push(ptr);
        ptr = ptr->next;
    }

    // print data from stack
    while (!stk.empty()) {
        cout << stk.top()->data << " ";
        stk.pop(); // pop after print
    }
    cout << "\n";
}

// Driver code
int main()
{
    // Start with the empty list
    struct Node* head = NULL;

    // Use push() to construct below list
    // 1->2->3->4->5
    push(&head, 5);
    push(&head, 4);
    push(&head, 3);
    push(&head, 2);
    push(&head, 1);

    // Function call
    printReverse(head);

    return 0;
}

Java

// Java program to print reverse of linked list
// using stack.
import java.util.*;

class GFG {

    /* Link list node */
    static class Node {
        int data;
        Node next;
    };

    /* Given a reference (pointer to pointer) to the head
    of a list and an int, push a new node on the front
    of the list. */
    static Node push(Node head_ref, int new_data)
    {
        Node new_node = new Node();
        new_node.data = new_data;
        new_node.next = (head_ref);
        (head_ref) = new_node;
        return head_ref;
    }

    /* Counts no. of nodes in linked list */
    static int getCount(Node head)
    {
        int count = 0; // Initialize count
        Node current = head; // Initialize current
        while (current != null) {
            count++;
            current = current.next;
        }
        return count;
    }

    /* Takes head pointer of the linked list and index
        as arguments and return data at index*/
    static int getNth(Node head, int n)
    {
        Node curr = head;
        for (int i = 0; i < n - 1 && curr != null; i++)
            curr = curr.next;
        return curr.data;
    }

    static void printReverse(Node head)
    {
        // store Node addresses in stack
        Stack<Node> stk = new Stack<Node>();
        Node ptr = head;
        while (ptr != null) {
            stk.push(ptr);
            ptr = ptr.next;
        }

        // print data from stack
        while (stk.size() > 0) {
            System.out.print(stk.peek().data + " ");
            stk.pop(); // pop after print
        }
        System.out.println("\n");
    }

    // Driver code
    public static void main(String args[])
    {
        // Start with the empty list
        Node head = null;

        // Use push() to construct below list
        // 1.2.3.4.5
        head = push(head, 5);
        head = push(head, 4);
        head = push(head, 3);
        head = push(head, 2);
        head = push(head, 1);

        // Function call
        printReverse(head);
    }
}

// This code is contributed by Arnab Kundu

Python3

# Python3 program to print reverse of linked list
# using stack.

# Node of a linked list


class Node:
    def __init__(self, next=None, data=None):
        self.next = next
        self.data = data

# Given a reference (pointer to pointer) to the head
# of a list and an int, push a new node on the front
# of the list.


def push(head_ref, new_data):

    new_node = Node()
    new_node.data = new_data
    new_node.next = (head_ref)
    (head_ref) = new_node
    return head_ref

# Counts no. of nodes in linked list


def getCount(head):

    count = 0  # Initialize count
    current = head  # Initialize current
    while (current != None):

        count = count + 1
        current = current.next

    return count

# Takes head pointer of the linked list and index
# as arguments and return data at index


def getNth(head, n):

    curr = head
    i = 0
    while(i < n - 1 and curr != None):
        curr = curr.next
        i = i + 1
    return curr.data


def printReverse(head):

    # store Node addresses in stack
    stk = []
    ptr = head
    while (ptr != None):

        stk.append(ptr)
        ptr = ptr.next

    # print data from stack
    while (len(stk) > 0):

        print(stk[-1].data, end=" ")
        stk.pop()  # pop after print

    print(" ")

# Driver code


# Start with the empty list
head = None

# Use push() to construct below list
# 1.2.3.4.5
head = push(head, 5)
head = push(head, 4)
head = push(head, 3)
head = push(head, 2)
head = push(head, 1)

# Function call
printReverse(head)

# This code is Contributed by Arnab Kundu

C#

// C# program to print reverse of linked list
// using stack.
using System;
using System.Collections.Generic;

class GFG {

    /* Link list node */
    public class Node {
        public int data;
        public Node next;
    };

    /* Given a reference (pointer to pointer) to the head
    of a list and an int, push a new node on the front
    of the list. */
    static Node push(Node head_ref, int new_data)
    {
        Node new_node = new Node();
        new_node.data = new_data;
        new_node.next = (head_ref);
        (head_ref) = new_node;
        return head_ref;
    }

    /* Counts no. of nodes in linked list */
    static int getCount(Node head)
    {
        int count = 0; // Initialize count
        Node current = head; // Initialize current
        while (current != null) {
            count++;
            current = current.next;
        }
        return count;
    }

    /* Takes head pointer of the linked list and index
        as arguments and return data at index*/
    static int getNth(Node head, int n)
    {
        Node curr = head;
        for (int i = 0; i < n - 1 && curr != null; i++)
            curr = curr.next;
        return curr.data;
    }

    static void printReverse(Node head)
    {
        // store Node addresses in stack
        Stack<Node> stk = new Stack<Node>();
        Node ptr = head;
        while (ptr != null) {
            stk.Push(ptr);
            ptr = ptr.next;
        }

        // print data from stack
        while (stk.Count > 0) {
            Console.Write(stk.Peek().data + " ");
            stk.Pop(); // pop after print
        }
        Console.WriteLine("\n");
    }

    // Driver code
    public static void Main(String[] args)
    {
        // Start with the empty list
        Node head = null;

        // Use push() to construct below list
        // 1.2.3.4.5
        head = push(head, 5);
        head = push(head, 4);
        head = push(head, 3);
        head = push(head, 2);
        head = push(head, 1);

        // Function call
        printReverse(head);
    }
}

// This code is contributed by Rajput-Ji

Javascript

<script>

// Javascript program to print reverse of linked list
// using stack.

/* Link list node */
class Node {

    constructor()
    {
        this.data = 0;
        this.next = null;
    }
};

/* Given a reference (pointer to pointer) to the head
of a list and an int, push a new node on the front
of the list. */
function push(head_ref, new_data)
{
    var new_node = new Node();
    new_node.data = new_data;
    new_node.next = (head_ref);
    (head_ref) = new_node;
    return head_ref;
}
/* Counts no. of nodes in linked list */
function getCount(head)
{
    var count = 0; // Initialize count
    var current = head; // Initialize current
    while (current != null) {
        count++;
        current = current.next;
    }
    return count;
}
/* Takes head pointer of the linked list and index
    as arguments and return data at index*/
function getNth(head, n)
{
    var curr = head;
    for (var i = 0; i < n - 1 && curr != null; i++)
        curr = curr.next;
    return curr.data;
}
function printReverse(head)
{
    // store Node addresses in stack
    var stk = [];
    var ptr = head;
    while (ptr != null) {
        stk.push(ptr);
        ptr = ptr.next;
    }
    // print data from stack
    while (stk.length > 0) {
        document.write(stk[stk.length-1].data + " ");
        stk.pop(); // pop after print
    }
    document.write("<br>");
}

// Driver code
// Start with the empty list
var head = null;
// Use push() to construct below list
// 1.2.3.4.5
head = push(head, 5);
head = push(head, 4);
head = push(head, 3);
head = push(head, 2);
head = push(head, 1);
// Function call
printReverse(head);


</script>

Output

5 4 3 2 1 

Time complexity: O(N) where N is number of nodes of linked list
Auxiliary Space: O(n)