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.next;
        head.next = null;
        while(p!=null){
            ListNode temp = p.next;
            p.next = head;
            head = p;
            p = temp;
        }
        return head;
    }
}