【LeetCode】2. 两数相加

public ListNode AddTwoNumbers(ListNode l1, ListNode l2)
{
    //若其中一个链表是0，返回另外一个
    if (l1.val == 0 && l1.next == null) return l2;

    if (l2.val == 0 && l2.next == null) return l1;

    //个位相加
    var sum = l1.val + l2.val;
    var isAddOne = sum > 9;
    var result = new ListNode(isAddOne ? sum % 10 : sum);
    var current = result;

    //循环相加
    while (true)
    {
        l1 = l1?.next;
        l2 = l2?.next;

        if (l1 == null && l2 == null) break;

        sum = (l1?.val ?? 0) + (l2?.val ?? 0) + (isAddOne ? 1 : 0); //考虑进位
        isAddOne = sum > 9;

        current.next = new ListNode(isAddOne ? sum % 10 : sum);
        current = current.next;
    }
    //最高位若有进位
    if (isAddOne)
    {
        current.next = new ListNode(1);
    }
    return result;
}