Program To Create A Singly Linked List Of N Nodes And Display It In Reverse Order

Program to create a singly linked list of n nodes and display it in reverse order

Explanation

In this program, we need to create a singly linked list and display the list in reverse order.

Original List

Program to create a singly linked list of n nodes and display it in reverse order

Reversed List

One of the approaches to solving this problem is to reach the end the of the list and display the nodes from tail to head recursively.

Algorithm

Create a class Node which has two attributes: data and next. Next is a pointer to the next node in the list.
Create another class which has two attributes: head and tail.
addNode() will add a new node to the list:
1. Create a new node.
2. It first checks, whether the head is equal to null which means the list is empty.
3. If the list is empty, both head and tail will point to the newly added node.
4. If the list is not empty, the new node will be added to end of the list such that tail's next will point to the newly added node. This new node will become the new tail of the list.
reverse() will reverse the order of the nodes present in the list.
1. This method checks whether node next to current is null which implies that, current is pointing to tail, then it will print the data of the tail node.
2. Recursively call reverse() by considering node next to current node and prints out all the nodes in reverse order starting from the tail.
display() will display the nodes present in the list:
1. Define a node current which will initially point to the head of the list.
2. Traverse through the list till current points to null.
3. Display each node by making current to point to node next to it in each iteration.

Solution

Python

#Represent a node of the singly linked list
class Node:
    def __init__(self,data):
        self.data = data;
        self.next = None;
        
class ReverseList:
    #Represent the head and tail of the singly linked list
    def __init__(self):
        self.head = None;
        self.tail = None;
        
    #addNode() will add a new node to the list
    def addNode(self, data):
        #Create a new node
        newNode = Node(data);
        
        #Checks if the list is empty
        if(self.head == None):
            #If list is empty, both head and tail will point to new node
            self.head = newNode;
            self.tail = newNode;
        else:
            #newNode will be added after tail such that tail's next will point to newNode
            self.tail.next = newNode;
            #newNode will become new tail of the list
            self.tail = newNode;
            
    #reverse() will the reverse the order of the list
    def reverse(self, current):
        #Checks if list is empty
        if(self.head == None):
            print("List is empty");
            return;
        else:
            #Checks if the next node is None, if yes then prints it.
            if(current.next == None):
                print(current.data ,end=" ");
                return;
            #Recursively calls the reverse function
            self.reverse(current.next);
            print(current.data ,end=" ");
    
    #display() will display all the nodes present in the list
    def display(self):
        #Node current will point to head
        current = self.head;
        
        if(self.head == None):
            print("List is empty");
            return;
            
        while(current != None):
            #Prints each node by incrementing pointer
            print(current.data , end=" ");
            current = current.next;
        print();
 
sList = ReverseList();
        
#Add nodes to the list
sList.addNode(1);
sList.addNode(2);
sList.addNode(3);
sList.addNode(4);
 
print("Original List: ");
sList.display();
 
print("Reversed List: ");
#Print reversed list
sList.reverse(sList.head);

Output:

Original List: 
1 2 3 4 
Reversed List: 
4 3 2 1

C

#include <stdio.h>
 
//Represent a node of the singly linked list
struct node{
    int data;
    struct node *next;
};    
 
//Represent the head and tail of the singly linked list
struct node *head, *tail = NULL;
 
//addNode() will add a new node to the list
void addNode(int data) {
    //Create a new node
    struct node *newNode = (struct node*)malloc(sizeof(struct node));
    newNode->data = data;
    newNode->next = NULL;
    
    //Checks if the list is empty
    if(head == NULL) {
        //If list is empty, both head and tail will point to new node
        head = newNode;
        tail = newNode;
    }
    else {
        //newNode will be added after tail such that tail's next will point to newNode
        tail->next = newNode;
        //newNode will become new tail of the list
        tail = newNode;
    }
}
 
//reverse() will the reverse the order of the list
void reverse(struct node *current) {
    //Checks if list is empty
    if(head == NULL) {
        printf("List is empty\n");
        return;
    }
    else{
        //Checks if the next node is null, if yes then prints it.
        if(current->next == NULL) {
            printf("%d ", current->data);
            return;
        }
        //Recursively calls the reverse function
        reverse(current->next);
        printf("%d ", current->data);
    }
}
    
//display() will display all the nodes present in the list
void display() {
    //Node current will point to head
    struct node *current = head;
    
    if(head == NULL) {
        printf("List is empty\n");
        return;
    }
    while(current != NULL) {
        //Prints each node by incrementing pointer
        printf("%d ", current->data);
        current = current->next;
    }
    printf("\n");
}
    
int main()
{
    //Add nodes to the list
    addNode(1);
    addNode(2);
    addNode(3);
    addNode(4);
    
    printf("Original List: \n");
    display();
    
    printf("Reversed List: \n");
    //Print reversed list
    reverse(head);
 
    return 0;
}

Output:

Original List: 
1 2 3 4 
Reversed List: 
4 3 2 1

JAVA

public class ReverseList {
    
    //Represent a node of the singly linked list
    class Node{
        int data;
        Node next;
        
        public Node(int data) {
            this.data = data;
            this.next = null;
        }
    }
 
    //Represent the head and tail of the singly linked list
    public Node head = null;
    public Node tail = null;
    
    //addNode() will add a new node to the list
    public void addNode(int data) {
        //Create a new node
        Node newNode = new Node(data);
        
        //Checks if the list is empty
        if(head == null) {
            //If list is empty, both head and tail will point to new node
            head = newNode;
            tail = newNode;
        }
        else {
            //newNode will be added after tail such that tail's next will point to newNode
            tail.next = newNode;
            //newNode will become new tail of the list
            tail = newNode;
        }
    }
    
    //reverse() will help the reverse the order of the list
    public void reverse(Node current) {
        //Checks if list is empty
        if(head == null) {
            System.out.println("List is empty");
            return;
        }
        else {
            //Checks if the next node is null, if yes then prints it.
            if(current.next == null) {
                System.out.print(current.data + " ");
                return;
            }
            //Recursively calls the reverse function
            reverse(current.next);
            System.out.print(current.data + " ");
        }
    }
        
    //display() will display all the nodes present in the list
    public void display() {
        //Node current will point to head
        Node current = head;
        
        if(head == null) {
            System.out.println("List is empty");
            return;
        }
        
        while(current != null) {
            //Prints each node by incrementing pointer
            System.out.print(current.data + " ");
            current = current.next;
        }
        System.out.println();
    }
    
    public static void main(String[] args) {
        
        ReverseList sList = new ReverseList();
        
        //Add nodes to the list
        sList.addNode(1);
        sList.addNode(2);
        sList.addNode(3);
        sList.addNode(4);
        
        System.out.println("Original List: ");
        sList.display();
        
        System.out.println("Reversed List: ");
        //Print reversed list
        sList.reverse(sList.head);
    }
}

Output:

Original List: 
1 2 3 4 
Reversed List: 
4 3 2 1

C#

using System;
                    
public class ReverseList
{
    //Represent a node of the singly linked list
    public class Node<T>{
        public T data;
        public Node<T> next;
        
        public Node(T value) {
            data = value;
            next = null;
        }
    }
        
    public class SinglyLinkedList<T>{
        //Represent the head and tail of the singly linked list
        public Node<T> head = null;             
         public Node<T> tail = null;
    
        //addNode() will add a new node to the list
        public void addNode(T data) {
            //Create a new node
            Node<T> newNode = new Node<T>(data);
 
            //Checks if the list is empty
            if(head == null) {
                //If list is empty, both head and tail will point to new node
                head = newNode;
                tail = newNode;
            }
            else {
                //newNode will be added after tail such that tail's next will point to newNode
                tail.next = newNode;
                //newNode will become new tail of the list
                tail = newNode;
            }
        }
        
        //reverse() will the reverse the order of the list
        public void reverse(Node<T> current) {
            //Checks if list is empty
            if(head == null) {
                Console.WriteLine("List is empty");
                return;
            }
            else{
                //Checks if the next node is null, if yes then prints it.
                if(current.next == null) {
                    Console.Write(current.data + " ");
                    return;
                }
                //Recursively calls the reverse function
                reverse(current.next);
                Console.Write(current.data + " ");
            }
        }
        
        //display() will display all the nodes present in the list
        public void display() {
            //Node current will point to head
            Node<T> current = head;
            
            if(head == null) {
                Console.WriteLine("List is empty");
                return;
            }
            
            while(current != null) {
                //Prints each node by incrementing pointer
                Console.Write(current.data + " ");
                current = current.next;
            }
            Console.WriteLine();
        }
    }
    
    public static void Main()
    {
        SinglyLinkedList<int> sList = new SinglyLinkedList<int>();
        
        //Add nodes to the list
        sList.addNode(1);
        sList.addNode(2);
        sList.addNode(3);
        sList.addNode(4);
        
        Console.WriteLine("Original List: ");
        sList.display();    
        
        Console.WriteLine("Reversed List: ");
        //Print reversed list
        sList.reverse(sList.head);
    }
}

Output:

Original List: 
1 2 3 4 
Reversed List: 
4 3 2 1

PHP

<!DOCTYPE html>
<html>
<body>
<?php
//Represent a node of singly linked list
class Node{
    public $data;
    public $next;
    
    function __construct($data){
        $this->data = $data;
        $this->next = NULL;
    }
}
class ReverseList{
    //Represent the head and tail of the singly linked list
    public $head;
    public $tail;
    function __construct(){
        $this->head = NULL;
        $this->tail = NULL;
    }
    
    //addNode() will add a new node to the list
    function addNode($data) {
        //Create a new node
        $newNode = new Node($data);
        
        //Checks if the list is empty
        if($this->head == NULL) {
            //If list is empty, both head and tail will point to new node
            $this->head = $newNode;
            $this->tail = $newNode;
        }
        else {
            //newNode will be added after tail such that tail's next will point to newNode
            $this->tail->next = $newNode;
            //newNode will become new tail of the list
            $this->tail = $newNode;
        }
    }
    
    //reverse() will the reverse the order of the list
    function reverse($current) {
        //Checks if list is empty
        if($this->head == NULL) {
            print("List is empty <br>");
            return;
        }
        else{
            //Checks if the next node is null, if yes then prints it.
            if($current->next == NULL) {
                print($current->data . " ");
                return;
            }
            //Recursively calls the reverse function
            $this->reverse($current->next);
            print($current->data . " ");
        }
    }
    
    //display() will display all the nodes present in the list
    function display() {
        //Node current will point to head
        $current = $this->head;
        
        if($this->head == NULL) {
            print("List is empty <br>");
            return;
        }
        while($current != NULL) {
            //Prints each node by incrementing pointer
            print($current->data . " ");
            $current = $current->next;
        }
        print("<br>");
    }
}
    
$sList = new ReverseList();
        
//Add nodes to the list
$sList->addNode(1);
$sList->addNode(2);
$sList->addNode(3);
$sList->addNode(4);
 
print("Original List: <br>");
$sList->display();
    
print("Reversed List: <br>");
//Print reversed list
$sList->reverse($sList->head);
?>
</body>
</html>

Output:

Original List: 
1 2 3 4 
Reversed List: 
4 3 2 1

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