题解 | #链表相加(二)#

class Solution {
  public:
    ListNode* addInList(ListNode* head1, ListNode* head2) {
        if (head1 == nullptr)
            return head2;
        if (head2 == nullptr)
            return head1;
        stack<unsigned char> v1;
        stack<unsigned char> v2;
        stack<unsigned char> ret;
        for (auto cur = head1; cur != nullptr;) {
            v1.push(cur->val);
            auto next_node = cur->next;
            delete cur;
            cur = next_node;
        }
        for (auto cur = head2; cur != nullptr;) {
            v2.push(cur->val);
            auto next_node = cur->next;
            delete cur;
            cur = next_node;
        }

        bool carry = false;
        while (!(v1.empty() && v2.empty())) {
            unsigned char a;
            unsigned char b;
            if (v1.empty())
                a = 0;
            else {
                a = v1.top();
                v1.pop();
            }
            if (v2.empty())
                b = 0;
            else {
                b = v2.top();
                v2.pop();
            }
            auto cur_num = a + b + (unsigned char)carry;
            if (cur_num >= 10) {
                carry = true;
                cur_num -= 10;
            } else
                carry = false;
            ret.push(cur_num);
        }
        if (carry)
            ret.push(1);

        ListNode* output = nullptr;
        auto cur = &output;
        while (!ret.empty()) {
            *cur = new ListNode(ret.top());
            ret.pop();
            cur = &((*cur)->next);
        }
        return output;
    }
};