leetcode 链表 206

//反转一个单链表。 
//
// 示例: 
//
// 输入: 1->2->3->4->5->NULL
//输出: 5->4->3->2->1->NULL 
//
// 进阶: 
//你可以迭代或递归地反转链表。你能否用两种方法解决这道题？ 
// Related Topics 链表 
// 👍 1507 👎 0


//leetcode submit region begin(Prohibit modification and deletion)
/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode reverseList(ListNode head) {
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        while(head != null && head.next != null){
            ListNode dnext = dummy.next;
            ListNode next = head.next;
            dummy.next = next;
            head.next = next.next;
            next.next = dnext;


        }
        return dummy.next;
    }
}
//leetcode submit region end(Prohibit modification and deletion)