java - Java中反转链表的程序

Question

我编写了以下代码，其中方法 rev(list,list) 不起作用。请帮我确定问题所在。

import java.io.*;
public class list
{
    int d;
    list l;
    list()
    {
        d=0;
        l=null;
    }

    void create()throws IOException
    {
        int n;// store number of nodes
        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        System.out.println("Enter the first data");
        this.d=Integer.parseInt(br.readLine());
        System.out.println("Enter number of nodes to be made");
        n=Integer.parseInt(br.readLine());
        list temp;
        list ptr=this;
        for(int i=1;i<n;i++)
        {
            temp=new list();
            System.out.println("Enter the next data");
            temp.d=Integer.parseInt(br.readLine());
            temp.l=null;
            ptr.l=temp;
            temp=null;
            ptr=ptr.l;
        }
    }

    void delete(list lst, int n)
    {
        list ptr=lst;
        list ptr1=ptr;
        int c=1;
        while(c<n)
        {
            ptr1=ptr;
            ptr=ptr.l;
            c++;
        }
        ptr1.l=ptr.l;
        ptr.l=null;
        ptr=null;
        ptr1=null;
    }

    void insertmid(list lst,int x, int n)
    {
        list temp=new list();
        temp.d=x;
        temp.l=null;
        list ptr=lst;
        int c=1;
        while(c<n)
        {
            ptr=ptr.l;
            c++;
        }
        temp.l=ptr.l;
        ptr.l=temp;
    }

    void rev(list lst,list lst1)
    {

        lst1=null;
        list ptr=new list();

        while(lst!=null)
        {
            ptr =lst;
            lst=lst.l;
            ptr.l=lst1;
            lst1=ptr;

        }
    }


    void display()
    {
        list ptr=this;

        while(ptr!=null)
        {
            System.out.print(ptr.d+"\t");
            ptr=ptr.l;
        }
        System.out.println();
    }

    public static void main(String args[])throws IOException
    {
        list l2=new list();
        list l3=new list();

        l2.create();
        l2.display();
        l2.insertmid(l2,14,2);
        l2.display();
        l2.delete(l2, 3);
        l2.display();
        l2.rev(l2,l3);
        l2.display();

    }
}

Answer 1

您应该做的第一件事就是熟悉 Java Naming Conventions因为它会让你的代码更干净、更容易理解。您当前的代码不区分类、方法或变量。

其次，看来您来自 C++ 背景，并且不知道 Java 总是 passes by value

这是您正在做的一件毫无意义的事情:

void rev(list lst,list lst1)
{

    lst1=null;  // this is pointless, essentially, you are using a passed argument as a local variable. 
    // ...

下面的代码实际上是等效的:

void rev(list lst)
{

    list lst1=null; //just create lst1 right here, don't need to pass it in as a parameter
    // ...

现在，我不会清理你的整个代码，但我会给你反向链接列表的算法，你可以将其合并到你的程序中:

public Node reverseList(Node head) {
    Node newHead = null;        // New head of the reversed list
    Node prev, curr, next;      // Tracker pointers to previous, current and next node
    prev = null;
    curr = head;
    next = null;
    while(curr != null) {       // Iterate through the list
        next = curr.next;       // Remember the next node
        curr.next = prev;       // Point the current node to the previous
        prev = curr;            // Update the previous node tracker to the current node
        curr = next;            // Update the current node tracker to the next node
        if(next == null) {      // If we reached list end, store the new head
            newHead = prev;
        }
    }
    return newHead;
}