16_反转链表

题目：输入一个链表的头结点，反转该链表并输出反转后链表的头结点。

import java.util.Scanner;class ListNode{    int value;    ListNode next;}public class Main{    //递归反转    private static ListNode reverse1(ListNode head) {        if(head == null || head.next == null)            return head;        ListNode nextNode = head.next;        head.next = null;        ListNode reverseRest = reverse1(nextNode);        nextNode.next = head;               return reverseRest;    }    //遍历反转    private static ListNode reverse2(ListNode cur) {        if(cur == null || cur.next == null)            return cur;             ListNode pre = null;// 上一结点        ListNode nextNode = null;// 下一结点        // 当前结点为null，说明位于尾结点        while(cur != null){            nextNode = cur.next;            cur.next = pre;// 反转指针域的指向             // 指针往下移动            pre = cur;            cur = nextNode;        }        return pre;    }    private static void printReverseList(ListNode head){        ListNode tempNode = head;        while(tempNode != null){            System.out.print(tempNode.value +" ");            tempNode = tempNode.next;        }    }    public static void main(String[] args) {        System.out.print("请输入单链表的节点数：");        Scanner in = new Scanner(System.in);        while (in.hasNext()) {                  ListNode node = new ListNode();            ListNode node1 = node;//用于输出原链表            ListNode node2 = node;//用于输出递归反转后的链表            ListNode node3 = node;//用于输出遍历反转后的链表            node.next = null;            int N = in.nextInt();//链表结点个数            if(N <= 0)                return;            System.out.print("请输入链表(以空格隔开)：");            for (int i = 0; i < N; i++) {                ListNode p = new ListNode();                p.value = in.nextInt();                p.next = null;                node.next = p;                node = node.next;            }                   System.out.print("原链表：");            printReverseList(node1.next);            System.out.println();            System.out.print("递归输出：");            printReverseList(reverse1(node2.next));            System.out.println();            //System.out.print("遍历输出：");            //printReverseList(reverse2(node3.next));        }        in.close();    }}