#include "s0002_add_two_numbers.hpp"

ListNode* S0002::addTwoNumbers(ListNode* l1, ListNode* l2) {
  ListNode *l_begin = new ListNode((l1->val + l2->val) % 10);
  ListNode *l_end = l_begin;
  int carry{ (l1->val + l2->val) >= 10 ? 1 : 0 };
  while (l1->next != nullptr || l2->next != nullptr || carry != 0) {
    if (l1->next == nullptr && l2->next != nullptr) {
      l1->next = new ListNode(0);
    } else if (l1->next != nullptr && l2->next == nullptr) {
      l2->next = new ListNode(0);
    } else if (l1->next == nullptr && l2->next == nullptr && carry != 0) {
      l1->next = new ListNode(0);
      l2->next = new ListNode(0);
    }
    l1 = l1->next;
    l2 = l2->next;
    l_end->next = new ListNode((l1->val + l2->val + carry) % 10);
    l_end = l_end->next;
    carry = (l1->val + l2->val + carry) >= 10 ? 1 : 0;
  }
  return l_begin;
}