题解 | #链表相加(二)#

/**
 * struct ListNode {
 *  int val;
 *  struct ListNode *next;
 *  ListNode(int x) : val(x), next(nullptr) {}
 * };
 */
class Solution {
  public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param head1 ListNode类
     * @param head2 ListNode类
     * @return ListNode类
     */
    ListNode* ReverseList(ListNode* head) {
        ListNode* cur = head;
        ListNode* pre = nullptr;
        while (cur != nullptr) {
            ListNode* temp = cur->next;
            cur->next = pre;
            pre = cur;
            cur = temp;
        }
        return pre;
    }
    ListNode* addInList(ListNode* head1, ListNode* head2) {
        if (head1 == nullptr) return head2;
        if (head2 == nullptr) return head1;

        head1 = ReverseList(head1);
        head2 = ReverseList(head2);

        int carry = 0;

        ListNode* res = new ListNode(0);
        ListNode* ans = res;

        while (head1 != nullptr || head2 != nullptr) {
            ListNode* temp = new ListNode(0);
            ans->next = temp;
            ans = temp;

            if (head1 != nullptr && head2 != nullptr) {
                temp->val = head1->val + head2->val + carry;
                if (temp->val >= 10) {
                    carry = 1;
                    temp->val = (temp->val) % 10;
                }else{
                    carry =0;
                }
                head1 = head1->next;
                head2 = head2->next;
            }
            else if (head1 == nullptr && head2 != nullptr) {
                temp->val = head2->val + carry;
                if (temp->val >= 10) {
                    carry = 1;
                    temp->val = (temp->val) % 10;
                }else{
                    carry =0;
                }
                head2 = head2->next;
            }
            else if (head1 != nullptr && head2 == nullptr) {
                temp->val = head1->val + carry;
                if (temp->val >= 10) {
                    carry = 1;
                    temp->val = (temp->val) % 10;
                }else{
                    carry =0;
                }
                head1 = head1->next;
            }
        }

        if (carry != 0) {
            ListNode* temp = new ListNode(carry);
            ListNode* ans = res;
            while (ans->next != nullptr) {
                ans = ans->next;
            }
            ans->next = temp;
        }

        return ReverseList(res->next);
    }
};