How to create a pointer to another pointer in a linked list?
Last Updated :
31 Jan, 2023
In this article we cover how to create a pointer to another pointer in a linked list, it can be singly, doubly, or circularly.
What is Linked List:
A linked list is a linear data structure, in which the elements are not stored at contiguous memory locations. The elements in a linked list are linked using pointers as shown in the below image:
Singly Linked List:
- In, a singly linked list, each node has a value and a pointer to the next node.
- It is of most common linked list.
- We can go only in one direction, head to tail.
Doubly Linked List:
- A Doubly Linked List (DLL) contains an extra pointer, typically called the previous pointer, together with the next pointer and data.
- We can go in both directions, head to tail and tail to head.
Circularly Linked List:
- The circular linked list is a linked list where all nodes are connected to form a circle.
- In a circular linked list, the first node and the last node are connected to each other which forms a circle.
- There is no NULL at the end.
How to create a pointer to another pointer in a linked list?
We can create a pointer to another pointer in a linked list by making a dummy node. Let’s say you want a pointer that should point to the head of the linked list. Usually, we create a dummy pointer with the value -1.
Below is the implementation:
C++
#include <iostream>
using namespace std;
class Node {
public:
int data;
Node* next;
Node(int data)
{
this->data = data;
this->next = NULL;
}
~Node()
{
int value = this->data;
if (this->next != NULL) {
delete next;
this->next = NULL;
}
}
};
void insertAtTail(Node*& tail, int d)
{
Node* temp = new Node(d);
tail->next = temp;
tail = temp;
}
void print(Node*& head)
{
Node* temp = head;
while (temp != NULL) {
cout << temp->data << " ";
temp = temp->next;
}
cout << endl;
}
Node* createPointer(Node*& head)
{
Node* dummy = new Node(-1);
dummy->next = head;
return dummy;
}
int main()
{
Node* node = new Node(1);
Node* head = node;
Node* tail = node;
insertAtTail(tail, 2);
insertAtTail(tail, 3);
insertAtTail(tail, 4);
insertAtTail(tail, 5);
cout << "Linked List: " << endl;
print(head);
Node* pt = createPointer(head);
cout
<< "Dummy pointer pointing to head of Linked List: "
<< endl;
print(pt);
return 0;
}
|
Java
import java.io.*;
class Node {
int data;
Node next;
public Node(int data)
{
this.data = data;
this.next = null;
}
}
class GFG {
static Node insertAtTail(Node tail, int d)
{
Node temp = new Node(d);
tail.next = temp;
tail = temp;
return temp;
}
static void printLL(Node head)
{
Node temp = head;
while (temp != null) {
System.out.print(temp.data + " ");
temp = temp.next;
}
System.out.println();
}
static Node createPointer(Node head)
{
Node dummy = new Node(-1);
dummy.next = head;
return dummy;
}
public static void main(String[] args)
{
Node node = new Node(1);
Node head = node;
Node tail = node;
tail = insertAtTail(tail, 2);
tail = insertAtTail(tail, 3);
tail = insertAtTail(tail, 4);
tail = insertAtTail(tail, 5);
System.out.println("Linked List: ");
printLL(head);
Node pt = createPointer(head);
System.out.println(
"Dummy pointer pointing to head of Linked List: ");
printLL(pt);
}
}
|
Python3
class Node:
def __init__(self, data):
self.data = data
self.next = None
def insertAtTail(tail, d):
temp = Node(d)
tail.next = temp
tail = temp
return temp
def printLL(head):
temp = head
while (temp != None):
print(temp.data,end=" ")
temp = temp.next
print()
def createPointer(head):
dummy = Node(-1)
dummy.next = head
return dummy
node = Node(1)
head = node
tail = node
tail = insertAtTail(tail, 2)
tail = insertAtTail(tail, 3)
tail = insertAtTail(tail, 4)
tail = insertAtTail(tail, 5)
print("Linked List: ")
printLL(head)
pt = createPointer(head)
print("Dummy pointer pointing to head of Linked List: ")
printLL(pt)
|
C#
using System;
public class Node {
public int data;
public Node next;
public Node(int data)
{
this.data = data;
this.next = null;
}
}
public class GFG {
static Node insertAtTail(Node tail, int d)
{
Node temp = new Node(d);
tail.next = temp;
tail = temp;
return temp;
}
static void printLL(Node head)
{
Node temp = head;
while (temp != null) {
Console.Write(temp.data + " ");
temp = temp.next;
}
Console.WriteLine();
}
static Node createPointer(Node head)
{
Node dummy = new Node(-1);
dummy.next = head;
return dummy;
}
static public void Main()
{
Node node = new Node(1);
Node head = node;
Node tail = node;
tail = insertAtTail(tail, 2);
tail = insertAtTail(tail, 3);
tail = insertAtTail(tail, 4);
tail = insertAtTail(tail, 5);
Console.WriteLine("Linked List: ");
printLL(head);
Node pt = createPointer(head);
Console.WriteLine(
"Dummy pointer pointing to head of Linked List: ");
printLL(pt);
}
}
|
Javascript
class Node {
constructor(data) {
this.data = data;
this.next = null;
}
}
function insertAtTail(tail, d) {
const temp = new Node(d);
tail.tail.next = temp;
tail.tail = temp;
}
function print(head) {
let temp = head;
while (temp != null) {
process.stdout.write(temp.data + ' ');
temp = temp.next;
}
console.log();
}
function createPointer(head) {
const dummy = new Node(-1);
dummy.next = head;
return dummy;
}
const node = new Node(1);
const head = node;
const tail = { tail: node };
insertAtTail(tail, 2);
insertAtTail(tail, 3);
insertAtTail(tail, 4);
insertAtTail(tail, 5);
console.log("Linked List:");
print(head);
const pt = createPointer(head);
console.log("Dummy pointer pointing to head of Linked List:");
print(pt);
|
Output
Linked List:
1 2 3 4 5
Dummy pointer pointing to head of Linked List:
-1 1 2 3 4 5
Time Complexity: O(1)
Auxiliary Space: O(1)
If you want to point to any other Node except the head then you have to first traverse to the node in the linked list. Then you can point the dummy pointer to it.
- Time for traversing: O(N)
- Time for creating the dummy node: O(1)
- Time to point it to the given node: O(1)
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