JAVA 双链表

/*
 * 不带头节点的
 */
public class Doublelinkedlist<T> {

    class node<T> {
        T data;
        node next, pre;

        public node() {
        }

        public node(T data) {
            this.data = data;
        }
    }

    private node<T> head;
    private node<T> tail;
    private int length;

    public Doublelinkedlist() {
        length = 0;
        head = null;
        tail = head;
    }

    boolean isEmpty() {
        return length == 0;
    }

    void addFirst(T data) {
        node<T> tmp = new node(data);
        if (isEmpty()) {
            head = tmp;
            tail = tmp;
        } else {
            tmp.next = head;
            head = tmp;
        }
        length++;
    }

    void addLast(T data)// 默认尾节点插入
    {
        node<T> tmp = new node(data);
        if (isEmpty()) {
            head = tmp;
            tail = tmp;
        } else {
            tail.next = tmp;
            tmp.pre = tail;
            tail = tmp;
        }
        length++;
    }

    int length() {
        return length;
    }

    T getElum(int index)// 为了简单统一从头找
    {
        if (index > length - 1) {
            System.out.println("index is wrong!!!");
            return null;
        }
        node<T> tmp = head;
        for (int i = 0; i < index; i++) {
            tmp = tmp.next;
        }
        return tmp.data;
    }

    void add(int index, T data)// 编号插入
    {
        if (index == 0) {
            addFirst(data);
            length++;

        } else if (index == length) {// 临界
            addLast(data);
            length++;

        } else {
            node<T> newpre = head;
            for (int i = 0; i < index - 1; i++) {
                newpre = newpre.next;
            }
            node<T> newnode = new node(data);
            newnode.next = newpre.next;
            newpre.next.pre = newnode;
            newpre.next = newnode;
            newnode.pre = newpre;
            length++;
        }
    }

    void deleteFirst()// 头部删除
    {
        if (length == 1) {// 临界
            head = null;
            tail = head;
            length--;

        } else {
            head.next.pre = null;
            head = head.next;
            length--;
        }
    }

    void deleteLast() {
        if (length == 1) {// 临界
            head = null;
            tail = head;
            length--;

        } else {
            tail.pre.next = null;
            tail = tail.pre;
            length--;
        }
    }

    void delete(int index) {
        if (index == 0) {
            deleteFirst();
        } else if (index == length - 1) {
            deleteLast();

        } else {
            node tmpp = head;
            for (int i = 0; i < index - 1; i++)
                tmpp = tmpp.next;
            tmpp.next.next.pre = tmpp;
            tmpp.next = tmpp.next.next;
            length--;
        }
    }

    void set(int index, T data) {
        node<T> tmpp = head;
        for (int i = 0; i < index - 1; i++)
            tmpp = tmpp.next;
        tmpp.data = data;

    }

    @Override
    public String toString() {
        String s = "";
        node tmpp = head;
        while (tmpp != null) {

            s += tmpp.data + " ";
            tmpp = tmpp.next;
        }
        return s;
    }

    public static void main(String[] args) {
        Doublelinkedlist<Integer> list = new Doublelinkedlist<Integer>();
        list.addLast(10);
        list.addFirst(20);
        list.add(1, 101);
        list.addLast(-10);
        list.addLast(30);
        list.addFirst(40);
        System.out.println(list.toString() + " length " + list.length());
        list.deleteFirst();
        System.out.println(list.toString() + " length " + list.length());
        System.out.println(list.toString() + " length " + list.length());
        list.delete(1);
        System.out.println(list.toString() + " length " + list.length());
        list.deleteLast();
        System.out.println(list.toString() + " length " + list.length());
        list.deleteFirst();
        System.out.println(list.toString() + " length " + list.length());
    }
}