C++ solution, easy to understand


  • 20
    H

    The trick is, when two lists are not equally long, pad the shorter one with zero values. In this way, you don't have to handle the remaining sublist.

    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;
    }

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