题目描述：

You are given two linked lists representing two non-negative numbers. 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.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

代码：

ListNode * Solution::addTwoNumbers(ListNode *l1, ListNode *l2)
{
    ListNode * node = new ListNode(0);
    ListNode * head = node;
    int carry = 0;
    while(l1 != NULL && l2 != NULL)
    {
        ListNode * newNode = new ListNode(0);
        int sum = l1->val + l2->val + carry;
        carry = sum / 10;
        sum = sum % 10;
        newNode->val = sum;
        node->next = newNode;
        node = node->next;
        l1 = l1->next;
        l2 = l2->next;
    }
    while(l1 != NULL)
    {
        ListNode * newNode = new ListNode(0);
        int sum = l1->val + carry;
        carry = sum / 10;
        sum = sum % 10;
        newNode->val = sum;
        node->next = newNode;
        node = node->next;
        l1 = l1->next;
    }
    while(l2 != NULL)
    {
        ListNode * newNode = new ListNode(0);
        int sum = l2->val + carry;
        carry = sum / 10;
        sum = sum % 10;
        newNode->val = sum;
        node->next = newNode;
        node = node->next;
        l2 = l2->next;
    }
    if(carry)
    {
        ListNode * newNode = new ListNode(0);
        newNode->val = 1;
        node->next = newNode;
    }
    return head->next;
}

LeetCode:Add Two Numbers