Description
You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.
You may assume the two numbers do not contain any leading zero, except the number 0 itself.
你有两个用链表代表的整数，其中每个节点包含一个数字。数字存储按照在原来整数中相反的顺序，使得第一个数字位于链表的开头。写出一个函数将两个整数相加，用链表形式返回和。
Examples
Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.
Answer
Add two numbers at the same position of each list and use another variable to store the carry.
Time Complexity
O(n)
Code
C++
class Solution {
public:
ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
if(!l1) return l2;
if(!l2) return l1;
int c = 0;
ListNode *head = new ListNode(0);
ListNode *ptr = head;
while(1)
{
if(l1)
{
c += l1->val;
l1 = l1->next;
}
if(l2)
{
c+= l2->val;
l2 = l2->next;
}
ptr->val = c % 10;
c /= 10;
if(l1 || l2 || c != 0)
ptr = (ptr->next = new ListNode(0));
else break;
}
return head;
}
};
