一、定义链表节点
class ListNode {
var val: Int
var next: ListNode?
init(_ val: Int) {
self.val = val
self.next = nil
}
}
二、反转方法
func reverList(headNode: ListNode) -> ListNode {
var pre: ListNode?
var next: ListNode?
var cur: ListNode? = headNode
while cur != nil { //cur 依次尾部移动， cur.next 总是pre ，中间变量next 为了记录cur要向前移动的位置。
next = cur?.next
cur?.next = pre
pre = cur
cur = next
}
// 循环结束的条件是cur == nil 所以头结点是pre
return pre!
}
三、 override func viewDidLoad() 中调用
override func viewDidLoad() {
let alist = ListNode(1)
let blist = ListNode(2)
let clist = ListNode(3)
let dlist = ListNode(4)
alist.next = blist
blist.next = clist
clist.next = dlist
let newlist = reverList(headNode: alist)
print("依次反转后-\(newlist.val)")
print("依次反转后-\(newlist.next!.val)")
print("依次反转后-\(newlist.next!.next!.val)")
print("依次反转后-\(newlist.next!.next!.next!.val)")
}
打印
依次反转后-4
依次反转后-3
依次反转后-2
依次反转后-1
