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
解法:
/**
* Definition for singly-linked list.
* public class ListNode {
* public var val: Int
* public var next: ListNode?
* public init(_ val: Int) {
* self.val = val
* self.next = nil
* }
* }
*/
class Solution {
func reverseList(_ head: ListNode?) -> ListNode? {
if(head == nil || head!.next == nil){
return head;
}
let res:ListNode = reverseList(head!.next)!;
head!.next!.next = head;
head!.next = nil;
return res;
}
}