我是Swift的新手，我无法弄清楚我解开了哪个可选变量，并给它分配了nil，我试图在Playground上对其进行调试，但它不允许我单步执行代码。
致命错误：展开一个可选值时意外发现nil
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 addTwoNumbers(_ l1: ListNode?, _ l2: ListNode?) -> ListNode? {
let result = ListNode()
var resultTail = result
var carry: Int = 0
var out: Int = 0
var val1: Int = 0
var val2: Int = 0
var head1: ListNode? = l1
var head2: ListNode? = l2
while (l1 != nil || l2 != nil || carry != 0) {
val1 = head1 != nil ? head1!.val : 0
val2 = head2 != nil ? head2!.val : 0
out = (val1 + val2 + carry) % 10
carry = (val1 + val2 + carry) / 10
resultTail.next = ListNode(out)
resultTail = resultTail.next!
head1 = head1?.next!
head2 = head2?.next!
}
return result.next!
}
}
let node3 = ListNode(3)
let node2 = ListNode(4, node3)
let node1 = ListNode(2, node2)
let node3a = ListNode(5)
let node2a = ListNode(6, node3a)
let node1a = ListNode(4, node2a)
let solution = Solution().addTwoNumbers(node1, node1a)
最好的祝福， 法罗斯
