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Add Two Numbers

Problem​

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 contains a single digit. Add the two numbers and return the sum as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Solution Approach​

Click - to see solution code
class Solution {
   public:
    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
        int carry = 0;
        ListNode root(0), *p = &root;
        while (l1 || l2 || carry) {
            int sm = (l1 ? l1->val : 0) + (l2 ? l2->val : 0) + carry;
            p->next = new ListNode(sm % 10);
            carry = sm / 10;
            l1 = (l1 ? l1->next : l1);
            l2 = (l2 ? l2->next : l2);
            p = p->next;
        }
        return root.next;
    }
};