题解 | 反转链表

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param head ListNode类 
     * @return ListNode类
     */
    public ListNode ReverseList (ListNode head) {
       if(head == null){
        return null;
       }
       ListNode pre = null;
       ListNode next = null;
       while(head != null){
        //继承head.next数据
        next = head.next;
        //指针反向 后续输出也是反着来
        head.next = pre;
        //后移
        pre = head;
		 //上面两步把next弄成pre 输出也是反着来的
		 
		 
        //后移
        head = next;
       }
	  //反着打印链表
    return pre;
}
}