LeetCode—链表反转

输入: 1->2->3->4->5->NULL
输出: 5->4->3->2->1->NULL

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public var val: Int
 *     public var next: ListNode?
 *     public init() { self.val = 0; self.next = nil; }
 *     public init(_ val: Int) { self.val = val; self.next = nil; }
 *     public init(_ val: Int, _ next: ListNode?) { self.val = val; self.next = next; }
 * }
 */
class Solution {
func reverseList(_ head: ListNode?) -> ListNode? {
var cur = head
var next = cur?.next
var pre : ListNode?
while (cur != nil) {
            next = cur?.next
            cur?.next = pre
            pre = cur
            cur = next
        }
return pre
    }
}