//不能用普通的整数类型来存储结果，因为这样用链表表示的数字可能是天文数字
public ListNode AddTwoNumbers(ListNode l1, ListNode l2)
{
ListNode head = new ListNode(int.MinValue);
ListNode current = head;
AddTwoHelper helper = new AddTwoHelper(0, current);
while (l1 != null && l2 != null)
{
AddTwoNumberInList(l1, l2, helper);
l1 = l1.next;
l2 = l2.next;
}
//链表长度不一样时，把长的多出来那截加上
while (l1 != null)
{
AddTwoNumberInList(l1, null, helper);
l1 = l1.next;
}
while (l2 != null)
{
AddTwoNumberInList(l2, null, helper);
l2 = l2.next;
}
if (helper.Carry != 0)
{
helper.CurrentPtr.next = new ListNode(helper.Carry);
}
return(head.next);
}
private void AddTwoNumberInList(ListNode node1, ListNode node2, AddTwoHelper helper)
{
int sum = 0;
if (node2 != null)
{
sum = node1.val + node2.val + helper.Carry;
}
else
{
sum = node1.val + helper.Carry;
}
helper.Carry = sum / 10;
sum = sum % 10;
helper.CurrentPtr.next = new ListNode(sum);
helper.CurrentPtr = helper.CurrentPtr.next;
}
