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| public class DoublyLinkedList<E> {
private int size;
private Node<E> head;
private Node<E> tail;
public DoublyLinkedList() {
head = new Node<>(null, null, null);
tail = new Node<>(null, null, null);;
head.next = tail;
tail.prev = head;
}
public void addAtIndex(int index, E e) {
indexCheck(index);
Node<E> prev;
if (index < size - index) {
prev = head;
for (int i = 0; i < index; i++) {
prev = prev.next;
}
} else {
prev = tail;
for (int i = 0; i < size - index; i++) {
prev = prev.prev;
}
}
Node<E> node = new Node<>(e, prev, prev.next);
prev.next = node;
node.prev = prev;
size++;
}
public void addAtHead(E e) {
Node<E> node = new Node<>(e, head, head.next);
head.next.prev = node;
head.next = node;
size++;
}
public void addAtTail(E e) {
Node<E> node = new Node<>(e, tail.prev, tail);
tail.prev.next = node;
tail.prev = node;
size++;
}
public E deleteAtIndex(int index) {
indexCheck(index);
Node<E> prev;
if (index < size - index) {
prev = head;
for (int i = 0; i < index; i++) {
prev = prev.next;
}
} else {
prev = tail;
for (int i = 0; i < size - index - 1; i++) {
prev = prev.prev;
}
}
Node<E> next = prev.next;
next.next.prev = prev;
prev.next = next.next;
size--;
return next.e;
}
public E get(int index) {
indexCheck(index);
Node<E> node;
if (index < size - index) {
node = head;
for (int i = 0; i < index + 1; i++) {
node = node.next;
}
} else {
node = tail;
for (int i = 0; i < size - index; i++) {
node = node.prev;
}
}
return node.e;
}
private void indexCheck(int index) {
if (index < 0 || index >size) {
throw new IllegalArgumentException();
}
}
@Override
public String toString() {
Node<E> node = head;
StringJoiner sj = new StringJoiner(",");
for (int i = 0; i < size; i++) {
node = node.next;
sj.add(String.valueOf(node.e));
}
return sj.toString();
}
private static class Node<E> {
E e;
Node<E> prev;
Node<E> next;
Node(E e, Node<E> prev, Node<E> node) {
this.e = e;
this.prev = prev;
this.next = node;
}
}
public static void main(String[] args) {
DoublyLinkedList<Integer> list = new DoublyLinkedList<>();
list.addAtHead(1);
list.addAtTail(3);
list.addAtIndex(1, 2);
System.out.println(list);
System.out.println(list.get(1));
System.out.println(list.deleteAtIndex(1));
System.out.println(list);
System.out.println(list.get(1));
}
}
|
