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DoublyLinkedList.java
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public class DoublyLinkedList {
private Node head;
private Node tail;
private class Node {
int data;
Node next;
Node prev;
Node(int data) {
this.data = data;
this.next = null;
this.prev = null;
}
}
// Method to insert a node at the beginning of the list
public void insertAtFirst(int data) {
Node newNode = new Node(data);
if (head == null) {
head = newNode;
tail = newNode;
} else {
newNode.next = head;
head.prev = newNode;
head = newNode;
}
}
// Method to insert a node at the end of the list
public void insertAtLast(int data) {
Node newNode = new Node(data);
if (tail == null) {
head = newNode;
tail = newNode;
} else {
newNode.prev = tail;
tail.next = newNode;
tail = newNode;
}
}
// Method to insert a node at a particular index
public void insertAt(int data, int index) {
if (index < 0) {
throw new IllegalArgumentException("Index must be non-negative.");
}
if (index == 0) {
insertAtFirst(data);
return;
}
Node newNode = new Node(data);
Node current = head;
int currentIndex = 0;
while (current != null && currentIndex < index - 1) {
current = current.next;
currentIndex++;
}
if (current == null) {
throw new IndexOutOfBoundsException("Index out of bounds.");
}
newNode.next = current.next;
if (current.next != null) {
current.next.prev = newNode;
}
newNode.prev = current;
current.next = newNode;
}
// Method to delete the first node
public void deleteFirst() {
if (head == null) {
return;
}
if (head == tail) {
head = null;
tail = null;
} else {
head = head.next;
head.prev = null;
}
}
// Method to delete the last node
public void deleteAtEnd() {
if (tail == null) {
return;
}
if (head == tail) {
head = null;
tail = null;
} else {
tail = tail.prev;
tail.next = null;
}
}
// Method to delete a node at a particular index
public void deleteAt(int index) {
if (index < 0) {
throw new IllegalArgumentException("Index must be non-negative.");
}
if (index == 0) {
deleteFirst();
return;
}
Node current = head;
int currentIndex = 0;
while (current != null && currentIndex < index) {
current = current.next;
currentIndex++;
}
if (current == null) {
throw new IndexOutOfBoundsException("Index out of bounds.");
}
if (current == tail) {
deleteAtEnd();
} else {
current.prev.next = current.next;
current.next.prev = current.prev;
}
}
// Method to display the elements of the list
public void display() {
Node current = head;
while (current != null) {
System.out.print(current.data + " <-> ");
current = current.next;
}
System.out.println("null");
}
public static void main(String[] args) {
DoublyLinkedList myList = new DoublyLinkedList();
myList.insertAtLast(1);
myList.insertAtLast(2);
myList.insertAtLast(3);
myList.display();
myList.insertAtFirst(0);
myList.display();
myList.insertAt(2, 2);
myList.display();
myList.deleteFirst();
myList.display();
myList.deleteAtEnd();
myList.display();
myList.deleteAt(1);
myList.display();
myList.deleteAt(0);
myList.display();
myList.deleteAt(0);
myList.display();
}
}