//主要改变的操作是add和remove
public void add(int index, E element) {
// TODO Auto-generated method stub
rangeCheekForAdd(index);
if (index == size) {
Node<E> oldLast = last;
last = new Node<>(oldLast, element, first);
if (oldLast == null) {
first = last;
first.next = first;
first.prev = first;
}else {
oldLast.next = last;
first.prev = last;
}
}else {
Node<E> next = node(index);
Node<E> prev = next.prev;
Node<E> node = new Node<>(prev, element, next);
next.prev = node;
prev.next = node;
if (next == first) { //index == 0
first = node;
}
}
size ++;
}
remove
public E remove(int index) {
// TODO Auto-generated method stub
rangeCheck(index);
Node<E> node = first;
if (size == 1) {
first = null;
last = null;
}else {
node = node(index);
Node<E> prev = node.prev;
Node<E> next = node.next;
prev.next = next;
next.prev = prev;
if (node == first) { // index == 0,删除第一个
first = next;
}
if (node == last) { //index == size - 1,删除最后一个
last = prev;
}
}
size --;
return node.element;
}
完整代码：
package com.weyan;
public class CircleLinkedList<E> implements List<E> {
private static final int ELEMENT_NOT_FOUND = -1;
private int size;
private Node<E> first;
private Node<E> last;
//内部类
private static class Node<E> {
E element;
Node<E> prev;
Node<E> next;
//构造函数
public Node(Node<E> prev,E element, Node<E> next) {
super();
this.element = element;
this.next = next;
this.prev = prev;
}
}
@Override
public void clear() {
// TODO Auto-generated method stub
size = 0;
first = null;
last = null;
}
@Override
public int size() {
// TODO Auto-generated method stub
return size;
}
@Override
public boolean isEmpty() {
// TODO Auto-generated method stub
return size == 0;
}
@Override
public boolean contains(E element) {
// TODO Auto-generated method stub
return indexOf(element) != ELEMENT_NOT_FOUND;
}
@Override
public void add(E element) {
// TODO Auto-generated method stub
add(size, element);
}
@Override
public E get(int index) {
// TODO Auto-generated method stub
return node(index).element;
}
@Override
public E set(int index, E element) {
// TODO Auto-generated method stub
Node<E> node = node(index);
E old = node.element;
node.element = element;
return old;
}
@Override
public void add(int index, E element) {
// TODO Auto-generated method stub
rangeCheekForAdd(index);
if (index == size) {
Node<E> oldLast = last;
last = new Node<>(oldLast, element, first);
if (oldLast == null) {
first = last;
first.next = first;
first.prev = first;
}else {
oldLast.next = last;
first.prev = last;
}
}else {
Node<E> next = node(index);
Node<E> prev = next.prev;
Node<E> node = new Node<>(prev, element, next);
next.prev = node;
prev.next = node;
if (next == first) { //index == 0
first = node;
}
}
size ++;
}
@Override
public E remove(int index) {
// TODO Auto-generated method stub
rangeCheck(index);
Node<E> node = first;
if (size == 1) {
first = null;
last = null;
}else {
node = node(index);
Node<E> prev = node.prev;
Node<E> next = node.next;
prev.next = next;
next.prev = prev;
if (node == first) { // index == 0,删除第一个
first = next;
}
if (node == last) { //index == size - 1,删除最后一个
last = prev;
}
}
size --;
return node.element;
}
@Override
public int indexOf(E element) {
// TODO Auto-generated method stub
Node<E> node = first;
if (element == null) {
for (int i = 0; i < size; i++) {
if (node.element == null) return i;
node = node.next;
}
}else {
for (int i = 0; i < size; i++) {
if (element.equals(node.element)) return i;
node = node.next;
}
}
return ELEMENT_NOT_FOUND;
}
/**
* 获取index位置对应的节点对象
* size >> 1 等于size/2
* size << 2 等于size*2
*/
private Node<E> node(int index) {
rangeCheck(index);
if (index < (size >> 1)) {
Node<E> node = first;
for (int i = 0; i < index; i++) {
node = node.next;
}
return node;
}else {
Node<E> node = last;
for (int i = size - 1; i > index; i--) {
node = node.prev;
}
return node;
}
}
private void outOfBounds(int index) {
throw new IndexOutOfBoundsException("Index:" + index + ",size:" + size);
}
private void rangeCheck(int index) {
// TODO Auto-generated method stub
if (index < 0 || index >= size) {
outOfBounds(index);
}
}
public void rangeCheekForAdd(int index) {
// TODO Auto-generated constructor stub
if (index < 0 || index > size) {
outOfBounds(index);
}
}
@Override
public String toString() {
// TODO Auto-generated method stub
StringBuilder stringBuilder = new StringBuilder();
stringBuilder.append("size=").append(size).append(",[");
Node<E> node = first;
for (int i = 0; i < size; i++) {
if (i != 0) {
stringBuilder.append(", ");
}
stringBuilder.append(node.element);
node = node.next;
}
stringBuilder.append("]");
return stringBuilder.toString();
}
}
验证结果：
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