单链表的反转

/**
 * @date: 2018/8/11
 * @description: leetcode第206题 翻转单链表
 * 地址：https://leetcode-cn.com/problems/reverse-linked-list/description/
 */
public class ReverseList{
    
    //链表结构
    public static class ListNode{
        int val;
        ListNode next;
        ListNode(int val){
            this.val = val;
        }
    }
    
    public ListNode reverseList(ListNode head){
        
        if(head == null){
            return null;
        }

        ListNode newHead = null;//用于遍历的指针
        while(head != null){//遍历原链表，每遍历一个节点就将其反转
            ListNode next = head.next;//对下一个要遍历的节点进行备份
            head.next = newHead;//反转
            newHead = head;
            head = next;
        }

        return newHead;
    }

    //测试函数
    public static void main(String[] args){
        ListNode head = new ListNode(1);
        head.next = new ListNode(2);
        head.next.next = new ListNode(3);
        head.next.next.next = new ListNode(4);
        head.next.next.next.next = new ListNode(5);
        printHead(head);

        System.out.println();

        System.out.print("反转后:");
        ListNode newHead = new ReverseList().reverseList(head);
        printHead(newHead);
    }

    //打印链表的函数
    private static void printHead(ListNode head){

        while(head != null){
            System.out.print(head.val + "->");
            head = head.next;
        }
        System.out.print("null");
    }
}

运行结果