LeetCode Algorithms2: add two numbers

LeetCode algorithms 2

Problem
You are given two linked lists representing two non-negative numbers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.
Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

Code (in swift)

/** * 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 addTwoNumbers(l1: ListNode?, _ l2: ListNode?) -> ListNode? {        var l1 = l1        var l2 = l2        if l1 == nil && l2 == nil{            return nil        }        var increase: Int = 0;        var node: ListNode! = ListNode(0)        let newList: ListNode! = node        while(l1 != nil || l2 != nil){            let sum:Int = increase + (l1 != nil ? l1!.val : 0) + (l2 != nil ? l2!.val : 0)             node.next = ListNode(sum % 10)            increase = sum / 10            node  = node.next            if l1 != nil {                l1 = l1!.next            }            if l2 != nil {                l2 = l2!.next            }        }        if increase != 0 {            node.next = ListNode(increase)        }        return newList.next    }}

Time complexity : O(max(m,n)). Assume that m and n represents the length of l1 and l2 respectively, the algorithm above iterates at most max(m,n) times.
Space complexity : O(max(m,n)). The length of the new list is at most max(m,n)+1.