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) {
        // write code here
          if(head == null){
               return null;
           }
    
           ListNode p = head,pre = null;
           while(p != null){ 
               ListNode next = p.next; 
               p.next = pre; 
               pre = p; 
               p = next;   
           }
           return pre; 
    }
}