题目：

题解：

func addTwoNumbers(l1, l2 *ListNode) (head *ListNode) {var tail *ListNodecarry := 0for l1 != nil || l2 != nil {n1, n2 := 0, 0if l1 != nil {n1 = l1.Vall1 = l1.Next}if l2 != nil {n2 = l2.Vall2 = l2.Next}sum := n1 + n2 + carrysum, carry = sum%10, sum/10if head == nil {head = &ListNode{Val: sum}tail = head} else {tail.Next = &ListNode{Val: sum}tail = tail.Next}}if carry > 0 {tail.Next = &ListNode{Val: carry}}return
}