leetcode 2 add two numbers - hello lifer

题干

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.

题解

class Solution {
public:
    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
        int carry = 0, sum = 0;
        ListNode* res = new ListNode(0);
        ListNode* cur = res;
        while(l1 != nullptr || l2 != nullptr)
        {
            sum = 0;
            if(l1 != nullptr) sum += l1->val, l1 = l1->next;   
            if(l2 != nullptr) sum += l2->val, l2 = l2->next;
            sum += carry;
            carry = sum / 10;
            cur->next = new ListNode(sum % 10);
            cur = cur->next;
        }
        if(carry > 0) cur->next = new ListNode(carry);
        
        return res->next;
    }
};