import java.util.*;

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

public class Solution {
    /**
     * 代碼中的類名、方法名、參數(shù)名已經(jīng)指定，請(qǐng)勿修改，直接返回方法規(guī)定的值即可
     *
     *
     * @param head ListNode類
     * @return ListNode類
     */
    public static ListNode ReverseList (ListNode head) {
        if (head == null || head.next == null) return head;
        ListNode pre=head;
        ListNode cur =pre.next;
        while(cur!=null){
            ListNode temp = cur.next;
            cur.next = pre;
            if (pre == head) pre.next = null;
            pre = cur;
            cur = temp;
        }
        return pre;
    }
}