如何检查一个元素是否存在于链表中?

Question

我必须检查一个元素是否存在于链接列表中?我编写了以下代码，但它没有返回正确的输出。我不知道我做错了什么。谁能告诉我在下面的代码做错了什么?期望的输出是假和真，但是我得到的输出是假和假。

package BasicList1;

import java.util.Vector;
public class BasicList1 implements ListInterface{
    static String[] testcase1 = {"3","1","2","6","7","4","5"};
    public static void main (String[] args){
        BasicList1 testInstance = new BasicList1();
        ListNode head = new ListNode(testcase1[0]);
        ListNode node = head;
        System.out.println(testInstance.elements(head));
        System.out.println(testInstance.hasElement(head, "9"));
        System.out.println(testInstance.hasElement(head,"4"));
    }
    public BasicList1 getBasicList(String data){
        return this;
    }
    //write your code here
    public Vector<String> elements(ListNode head){
        ListNode temp=head;
        Vector v=new Vector();
        while(temp!=null){
            v.addElement(temp);
            temp=temp.next;
        }
        return v;
    }
    @Override
    public boolean hasElement(ListNode head, String data) {
        ListNode temp=head;
        while(temp!=null){
            if(temp.data.equals(data)){
                return true;
            }
            temp=temp.next;
        }
        return false;
    }

Answer 1

我不知道你的错误输出是什么，但我猜你的ListNode只包含一个元素:3.

这只创建一个包含testcase1[0](即"3")的单个节点的ListNode:

ListNode head = new ListNode(testcase1[0]);

因此，要初始化ListNode，你应该这样写:

ListNode head = new ListNode(testcase1[testcase1.length - 1]); 
for (int i = testcase1.length - 2; i >= 0; i--) {
     final ListNode tail = head;
     head = new ListNode(testcase1[i]);
     head.next = tail;
}

NodeList以相反的顺序构建，以避免遍历整个列表以在末尾添加元素。

编辑

你的elements方法也有问题。您正在添加ListNode而不是其内容，因此替换

v.addElement(temp);

v.addElement(temp.data);

编辑2

此外，BasicList1的设计相当糟糕:它不是真正面向对象的。你应该有这样的内容:

package test;
import java.util.Vector;
public class BasicList1 {
    private ListNode head;
    public BasicList1(String[] data) {
        if (data.length != 0 ) {
            head = new ListNode(data[data.length - 1]);
        }
        for (int i = data.length - 2; i >= 0; i--) {
            final ListNode tail = head;
            head = new ListNode(data[i]);
            head.next = tail;
        }
    }
    public BasicList1 getBasicList() {
        return this;
    }
    //write your code here
    public Vector<String> elements(){
        ListNode temp = head;
        Vector<String> v=new Vector<String>();
        while(temp!=null){
            v.addElement(temp.data);
            temp=temp.next;
        }
        return v;
    }
    @Override
    public boolean hasElement(String data) {
        ListNode temp=head;
        while(temp!=null){
            if(temp.data.equals(data)){
                return true;
            }
            temp=temp.next;
        }
        return false;
    }
    public static void main (String[] args){
        final String[] testcase1 = {"3","1","2","6","7","4","5"};
        final BasicList1 testInstance = new BasicList1(testcase1);
        System.out.println(testInstance.elements());
        System.out.println(testInstance.hasElement("9"));
        System.out.println(testInstance.hasElement("4"));
    }
}