2. Add Two Numbers

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.

Example:

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.

AC code:

/**
 * 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 *head = NULL, *prev = NULL;
        int carry = 0;
        while (l1 || l2) {
            int v1 = l1? l1->val: 0;
            int v2 = l2? l2->val: 0;
            int tmp = v1 + v2 + carry;
            carry = tmp / 10;
            int val = tmp % 10;
            ListNode* cur = new ListNode(val);
            if (!head) head = cur;
            if (prev) prev->next = cur;
            prev = cur;
            l1 = l1? l1->next: NULL;
            l2 = l2? l2->next: NULL;
        }
        if (carry > 0) {
            ListNode* l = new ListNode(carry);
            prev->next = l;
        }
        return head;
    }
};