定义一个函数，输入一个链表的头节点，反转该链表并输出反转后链表的头节点。
示例:
输入: 1->2->3->4->5->NULL
输出: 5->4->3->2->1->NULL限制：
0 <= 节点个数 <= 5000
//leetcode submit region begin(Prohibit modification and deletion)
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) { val = x; }
* }
*/
class Solution {
public ListNode reverseList(ListNode head) {
return reverseFunc(head);
}
private ListNode reverseFunc(ListNode node) {
if (node == null || node.next == null) {
return node;
}
ListNode nextNode = node.next;
node.next = null;
ListNode newHead = reverseFunc(nextNode);
nextNode.next = node;
return newHead;
}
}
//leetcode submit region end(Prohibit modification and deletion)
