从尾到头打印一个链表

Posted 2020-10-17 丹丹Jordan

1、利用jdk的链表数据结构实现：

    /**
     *  问题7、从尾到头打印列表 用jdk的LinkList
     *
     */
    @Test
    public void print_reverse_LinkedList(){
        LinkedList<Person> list = new LinkedList<Person>();
        for (int i =5;i>0;i--){
            Person p1 = new Person();
            p1.setName("Alice"+i);
            p1.setAge(10+i);
            list.add(p1);
        }

        // 利用栈 实现逆序打印链表的内容
        Stack<Person> stack = new Stack<Person>();
        while (!list.isEmpty()){
            Person p2 = list.getFirst();
            list.removeFirst();
            stack.push(p2);
        }

        while (!stack.isEmpty()){
            Person p = stack.pop();
            System.out.println(p.toString());
        }
       
    }

 2、自定义单链表，实现从尾到头打印链表

2.1数据结构的定义：

2.1.1链表的定义：

package com.itmei.offer;

/**
 * Created by qiaodan on 2017/12/8.
 */
public class MyLinkedList<T> {
    int size;
    MyLinkedListNode<T> head;
    MyLinkedListNode<T> rear;

    public MyLinkedListNode<T> getRear() {
        return rear;
    }

    public void setRear(MyLinkedListNode<T> rear) {
        this.rear = rear;
    }

    public int getSize() {
        return size;
    }

    public void setSize(int size) {
        this.size = size;
    }

    public MyLinkedListNode<T> getHead() {
        return head;
    }

    public void setHead(MyLinkedListNode<T> head) {
        this.head = head;
    }

    public MyLinkedList() {
        this.size = 0;
        this.head= null;
        this.rear = null;
    }

    public MyLinkedList add(T t){
        MyLinkedListNode<T> node = new MyLinkedListNode<>(t);
        if (this.head==null){
            this.head = node;
            this.size = 1;
            this.rear = node;
            return this;
        }else {
            this.rear.next = node;
            this.rear = node;
            this.size = this.size+1;
            return this;
        }
    }

    public boolean isEmpty(){
        if (this.size==0&&this.head==null) return true;
        else return false;
    }

    public T getFirst(){
        if (this.head!=null&&this.size>0)
            return this.head.getData();
        else return null;
    }

    public boolean removeFirst(){
        if (this.head.next==null){
            this.head =null;
            this.size =0;
            return true;
        }else {
            this.head =  this.head.next;
            this.size= this.size-1;
            return true;
        }
    }
}

 2.1.2链表节点的定义：

package com.itmei.offer;

/**
 * Created by qiaodan on 2017/12/8.
 */
public class MyLinkedListNode<T> {
    T data;
    MyLinkedListNode<T> next;

    public T getData() {
        return data;
    }

    public void setData(T data) {
        this.data = data;
    }

    public MyLinkedListNode<T> getNext() {
        return next;
    }

    public void setNext(MyLinkedListNode<T> next) {
        this.next = next;
    }

    public MyLinkedListNode(T data) {
        this.data = data;
        this.next = null;
    }


}

 2.2 倒叙遍历的实现：

2.2.1实现的主方法：

    /**
     *  问题8、从尾到头打印列表 自定义的MyLinkList 有next指针 可以直接用递归的方式来打印链表
     *
     */
    @Test
    public void print_reverse_MyLinkedList() {
        MyLinkedList<Person> list = new MyLinkedList<>();
        for (int i = 5; i > 0; i--) {
            Person p1 = new Person();
            p1.setName("Alice" + i);
            p1.setAge(10 + i);
            list.add(p1);
        }

        // 利用递归来打印
        if (list==null){
            System.out.println("链表为空！");
        }else {
            print_reverse_MyLinkedList(list.head);
        }

    }

 2.2.2实现的核心递归方法：

    // 递归动作 这里还有一个问题 为什么没有按照预期 倒叙打印 反而只打印了链表的尾部 一个else的区别 递归打印下面的元素之后 回来要打印自己！
    public void print_reverse_MyLinkedList(MyLinkedListNode head){
        if (head.next!=null)
            this.print_reverse_MyLinkedList(head.next);
         System.out.println(head.getData().toString());
    }