java - 为什么我无法将元素插入到我的链表实现中？

Question

我正在用java做链表实现。特别是，在执行插入操作时，如果给定的索引大于链表的长度，我必须将该值追加到链表中。尽管我已经为此编写了代码，但事情并没有这样发生。

为了调试这个，我添加了用于打印链接列表的行。我可以在插入函数中的条件 if(index >= this.length()) 之前打印列表，但无法在条件内的行中打印链接列表。

package com.learning.algorithms.LinkedList;

public class Node {
    int data;
    Node next;

    public Node() {
    }

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

package com.learning.algorithms.LinkedList;

public class LinkedList {
    Node head;
    Node tail;

    public LinkedList() {
        this.head = new Node();
        this.tail = this.head;
    }

    public LinkedList(int value) {
        this.head = new Node();
        this.head.data = value;
        this.head.next = null;
        this.tail = this.head;
    }

    public LinkedList append(int value) {
        Node newNode = new Node(value);
        this.tail.next = newNode;
        this.tail = newNode;

        return this;
    }

    public void printList() {
        Node useNode = this.head;

        while(useNode!=null)
        {
            System.out.println(useNode.data);
            useNode = useNode.next;
        }

        //print(useNode);
    }

    private void print(Node useNode) {
        if(useNode!=null)
        {
            System.out.println(useNode.data);
            print(useNode.next);
        }       
    }

    public LinkedList prepend(int i) {
        Node newNode = new Node(i);
        newNode.next = this.head;
        this.head  = newNode;
        return this;
    }

    public LinkedList insert(int index, int value) {
        if(index == 0)
        {
            this.prepend(value);
            return this;
        }

        this.printList();
        if(index >= this.length())
        {
            System.out.println("inside");
            this.printList();
            this.append(value);
            return this;
        }

        Node nodeJustBeforeGivenIndex = this.head;

        // getting node just before given index using while loop
        while(index>1)
        {
            nodeJustBeforeGivenIndex = nodeJustBeforeGivenIndex.next;
            index--;
        }

        // make an insert
        Node newNode = new Node(value);
        newNode.next = nodeJustBeforeGivenIndex.next;
        nodeJustBeforeGivenIndex.next = newNode;

        return this;
    }

    private int length() {
        int counnt = 0;

        if(this.head !=null ) {
            while(this.head !=null )
            {
                this.head = this.head.next;
                counnt++;
            }
        }

        return counnt;
    }
}

package com.learning.algorithms.LinkedList;

public class LinkedListImplementation {
    public static void main(String[] args)
    {
        LinkedList list = new LinkedList(10);

        list.append(5);
        list.append(16);
        list.prepend(1);
        list.insert(0, 15);
        list.insert(10, 222);

        list.printList();
    }
}

运行此实现类的控制台输出:

15
1
10
5
16
inside

Answer 1

您不应修改 length 方法内的 head 值。

这将解决它:

private int length() {
    int counnt = 0;

    Node iter = this.head;
    while(iter !=null )
    {
        iter = iter.next;
        counnt++;
    }

    return counnt;
}

仅注释插入内的两个打印状态，输出为:

inside
15
1
10
5
16
222