LeetCode2.cpp

/**
 *Definition for singly-linked list.
 *struct ListNode {
 *  int val;
 *  ListNode * next;
 *  ListNode() : val(0), next(nullptr) {}
 *  ListNode(int x) : val(x), next(nullptr) {}
 *  ListNode(int x, ListNode *next) : val(x), next(next) {}
 *};
 */
class Solution
{
public:
    ListNode *addTwoNumbers(ListNode *l1, ListNode *l2)
    {
        ListNode *dummyHead = new ListNode(0);
        ListNode *tail = dummyHead;
        int carry = 0;
        while (l1 != nullptr or l2 != nullptr or carry != 0)
        {
            int v1 = (l1 != nullptr) ? l1->val : 0;
            int v2 = (l2 != nullptr) ? l2->val : 0;
            int sum = v1 + v2 + carry;
            int digit = sum % 10;
            carry = sum / 10;
            ListNode *node = new ListNode(digit);
            tail->next = node;
            tail = tail->next;
            l1 = (l1 != nullptr) ? l1->next : nullptr;
            l2 = (l2 != nullptr) ? l2->next : nullptr;
        }
        ListNode *result = dummyHead->next;
        delete dummyHead;
        return result;
    }
};