LeetCode Add Two Numbers

before_5pm_challenge_add-two-numbers.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* res = new ListNode;
        ListNode *res_cpy = res;
        ListNode *l1_cpy = l1, *l2_cpy = l2; // So that l1 and l2 are not mutated
        int curry = 0;
        while (l1_cpy != nullptr || l2_cpy != nullptr) {
            int sum = 0;
            if (l1_cpy != nullptr) {
                sum += l1_cpy->val;
                l1_cpy = l1_cpy->next;
            }
            if (l2_cpy != nullptr) {
                sum += l2_cpy->val;
                l2_cpy = l2_cpy->next;
            }
            sum += curry;
            res_cpy->val = sum%10;
            curry = sum/10;
            if (l1_cpy == nullptr && l2_cpy == nullptr) {
                if (curry) res_cpy->next = new ListNode(curry);
                break;
            }
            res_cpy->next = new ListNode;
            res_cpy = res_cpy->next;
        }
        return res;
    }
};