[数据结构与算法]完成双链表的增删改查

下面是定义Node类，双链表和单链表是差不多的，只是双链表的对象中多了一个prev的概念，prev是该节点的前一个节点，next和单链表一个代表着该节点的下一个节点。

一下是双链表的定义类和对双链表操作的一些方法，

class Node {
    public int data;
    public Node prev;
    public Node next;

    public Node() {

    }

    public Node(int data) {
        this.data = data;
    }

    public Node head;
    public Node tail;

    //头插法
    public void addFirst(int data) {
        Node node = new Node(data);
        if (this.head == null) {
            this.head = node;
            this.tail = node;
            return;
        }
        node.next = this.head;
        this.head.prev = node;
        this.head = node;


    }

    //尾插法
    public void addLast(int data) {
        Node node = new Node(data);
        if (this.head == null) {
            this.head = node;
            this.tail = node;
            return;
        }
        Node cur = this.head;
        while (cur != tail) {
            cur = cur.next;
        }
        this.tail.next = node;
        node.prev = this.tail;
        this.tail = node;
    }

    public boolean check(int index) {
        if (index < 0 || index > size()) {
            return true;
        }
        return false;
    }

    //任意位置插入,第一个数据节点为0号下标
    public void addIndex(int index, int data) {
        Node node = new Node(data);
        if (check(index)) {
            throw new RuntimeException("超过范围");
        }
        if (index == 0) {
            addFirst(data);
        } else if (index == size()) {
            addLast(data);
        } else {
            Node cur = this.head;
            while (index > 1) {
                cur = cur.next;
                index--;
            }
            cur.next.prev = node;
            node.next = cur.next;
            node.prev = cur;
            cur.next = node;
        }
    }

    //查找是否包含关键字key是否在单链表当中
    public boolean contains(int key) {
        Node cur = this.head;
        while (cur != null) {
            if (cur.data == key) {
                return true;
            }
            cur = cur.next;
        }
        return false;
    }

    //删除第一次出现关键字为key的节点
    public void remove(int key) {
        Node cur = this.head;
        if (contains(key)) {
            if (this.head.data == key) {
                this.head = this.head.next;
            } else if (this.tail.data == key) {
                this.tail = this.tail.prev;
                this.tail.next = null;
            } else if (this.head == this.tail) {
                this.head = null;
            } else {
                while (cur != null) {
                    if (cur.data == key) {
                        cur.next.prev = cur.prev;
                        cur.prev.next = cur.next;
                    }
                    cur = cur.next;
                }
            }

        } else {
            System.out.println("不存在key");
        }
    }

    //删除所有值为key的节点
    public void removeAllKey(int key) {
        Node cur = this.head;
        if (contains(key)) {
            while (cur != null) {
                if (this.head.data == key) {
                    this.head = this.head.next;
                } else {
                    cur.next.prev=cur.prev;
                    cur.prev.next =cur.next;
                }
                cur = cur.next;
            }
        } else {
            System.out.println("不存在");
        }
    }

    //得到单链表的长度
    public int size() {
        Node cur = this.head;
        int cnt = 0;
        while (cur != null) {
            cur = cur.next;
            cnt++;
        }
        return cnt;
    }

    public void display() {
        Node cur = this.head;
        while (cur != null) {
            System.out.print(cur.data);
            cur = cur.next;
        }
        System.out.println();
    }

    public void clear() {
        while (this.head!=null){
            Node cur=this.head.next;

            this.head.next=null;

            this.head.prev=null;
            this.head=cur;
        }
    }
}

下面是main方法，写了一些对双链表的操作：

public class Test {
    public static void main(String[] args) {
         Node node = new Node();
        //利用循环调用头插法，把数据插入到链表中
        for (int i = 0; i < 5; i++) {
            node.addFirst(i);
        }
        node.display();//打印双链表
        System.out.println(node.size());//打印链表大小
        node.addIndex(2, 7);//2位置插入7
        node.addIndex(2, 7);//2位置插入7

        node.display();//打印双链表
        System.out.println(node.contains(0));//判断是否包含0；
        //remove是移除出现的第一个元素
        node.remove(4);
        node.remove(2);
        node.remove(1);
        node.remove(0);
        node.remove(3);
        node.remove(7);
        //因为元素都被移除了，再加一些元素进去
        node.addFirst(7);
        node.addFirst(7);
        node.addFirst(7);
        node.display();
        node.removeAllKey(7);
        node.display();

        for (int i = 0; i < 5; i++) {
            node.addFirst(i);
        }
        node.display();
        node.clear();//清空链表
        node.display();
    }
}