/// "两数相加"

/**
 * 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; }
 * }
 */

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 lH = l1
        var rH = l2
        var head = result
        
        var carry = 0
        
        while lH != nil || rH != nil {
            let sum = (lH?.val ?? 0) + (rH?.val ?? 0)
            carry = sum / 10
            head.next = ListNode(sum % 10)
            head = head.next!
            lH = lH?.next
            rH = rH?.next
        }
        
        if carry > 0 {
            head.next = ListNode(carry)
        }
        return head.next
    }
}