06-双向循环链表

//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：