LeetCode 第206题 反转链表

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？

class Solution206 {  2 
  //迭代
  public ListNode reverseList(ListNode head) {  5     ListNode dummyHead = new ListNode(0);  6     dummyHead.next = head;  7     ListNode node = head;  8     ListNode newDummyHead = new ListNode(0);  9 
    while (node != null) { 11       dummyHead.next = node.next; 12       node.next = newDummyHead.next; 13       newDummyHead.next = node; 14       node = dummyHead.next; 15  } 16     return newDummyHead.next; 17  } 18 
  //递归
  public ListNode reverseList_2(ListNode head) { 21     if (head == null || head.next == null) { 22       return head; 23  } 24     ListNode newHead = reverseList_2(head.next); 25     head.next.next = head; 26     head.next = null; 27     return newHead; 28 
 } 30 
}