一开始本想用函数把两个链表代表的数字都加起来，然后再取每一位数字合成链表，结果发现因为数字位数太多类似大整数，无法直接求出和，所以必须每一位都相加然后组成链表。
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
ListNode* s;
s = NULL;
ListNode* curs;
int sum = 0;
while (l1 != NULL || l2 != NULL)
{
if (l1 != NULL)
{
sum += l1->val;
l1 = l1->next;
}
if (l2 != NULL)
{
sum += l2->val;
l2 = l2->next;
}
if (s == NULL)
{
s = new ListNode(sum % 10);
curs = s;
}
else
{
curs->next = new ListNode(sum % 10);
curs = curs->next;
}
sum /= 10;
}
if (sum == 1)
{
curs->next = new ListNode(1);
}
return s;
}
};
原文：https://www.cnblogs.com/legendcong/p/9692430.html