1.3.30

import edu.princeton.cs.algs4.*;

public class Linklist
{
     private static class Node//节点
    {
        String item;
        Node next = null;
    }
    
     public Node create(int n)//创建链表
    {
        Node head = null;
        Node p1 = head;
        Node p2;
        for(int i = 0; i < n; i++)
        {
            p2 = new Node();
            StdOut.println("input the string of node " + i + ":");
            p2.item = StdIn.readString();
            if(head == null)
            {
               head = p1 = p2;
            }
            else
            {
               p1.next = p2;
               p1 = p2;
            }
        }
        if(head != null)
        {
           p1.next = null;
        }
        return head;
    }
   
    public void show(Node head)//遍历链表
    {
        Node current = head;
        while(current != null)
        {
            StdOut.print(current.item + "\t");
            current= current.next;
        }
        StdOut.print("\n");
    }
    
    public Node reverse(Node head)
    {
        Node first = head.next;
        Node second = head;
        Node temp;
        second.next = null;
        while(first != null)//可以花图思考
        {
            temp = first.next;
            first.next = second;
            second = first;
            first = temp;
        }
        return second;//到达边界时first变成了null,实际上second才是new_first
    }
    
    public static void main(String[] args)
    {
        Node old_head;
        int n;
        Linklist linklist = new Linklist();
        StdOut.println("input the length of linklist:(>0)");
        n = StdIn.readInt();
        old_head = linklist.create(n);
        linklist.show(old_head);
        Node new_head = linklist.reverse(old_head);
        linklist.show(new_head);
    }
}

import edu.princeton.cs.algs4.*;

public class Linklist
{
    private static class Node//节点
    {
        String item;
        Node next = null;
    }
    
     public Node create(int n)//创建链表
    {
        Node head = null;
        Node p1 = head;
        Node p2;
        for(int i = 0; i < n; i++)
        {
            p2 = new Node();
            StdOut.println("input the string of node " + i + ":");
            p2.item = StdIn.readString();
            if(head == null)
            {
               head = p1 = p2;
            }
            else
            {
               p1.next = p2;
               p1 = p2;
            }
        }
        if(head != null)
        {
           p1.next = null;
        }
        return head;
    }
   
    public void show(Node head)//遍历链表
    {
        Node current = head;
        while(current != null)
        {
            StdOut.print(current.item + "\t");
            current= current.next;
        }
        StdOut.print("\n");
    }
    
    public Node reverse(Node head)//我也不是很明白递归
    {
        if(head.next == null)
            return head;
        Node second = head.next;
        Node rest = reverse(second);
        second.next = head;
        head.next = null;
        return rest;
    }
    
    public static void main(String[] args)
    {
        Node head;
        int n;
        Linklist linklist = new Linklist();
        StdOut.println("input the length of linklist:(>0)");
        n = StdIn.readInt();
        head = linklist.create(n);
        linklist.show(head);
        head = linklist.reverse(head);
        linklist.show(head);
    }
}