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* addInList(ListNode* head1, ListNode* head2) {
        // write code here
        auto GetStackData = [](ListNode * node) -> stack<ListNode*> {
            stack<ListNode*> s;
            while (node != nullptr) {
                s.push(node);
                node = node->next;
            }
            return s;
        };

        auto s1 = GetStackData(head1);
        auto s2 = GetStackData(head2);

        if (s1.empty()) {
            return head2;
        } else if (s2.empty()) {
            return head1;
        }

        auto fake = ListNode(0);
        ListNode* cur = &fake;
        int cross = 0;
        while (!s1.empty() && !s2.empty()) {
            auto sum = s1.top()->val + s2.top()->val + cross;
            cross = 0;
            if (sum > 9) {
                sum -= 10;
                cross = 1;
            }
            auto new_node = new ListNode(sum);
            new_node->next = cur->next;
            cur->next = new_node;
            s1.pop();
            s2.pop();
        }


        if (s1.empty()) {
            while (!s2.empty()) {
                auto sum = s2.top()->val + cross;
                cross = 0;
                if (sum > 9) {
                    sum -= 10;
                    cross = 1;
                }
                auto new_node = new ListNode(sum);
                new_node->next = cur->next;
                cur->next = new_node;
                s2.pop();
            }
        } else {
            while (!s1.empty()) {
                auto sum = s1.top()->val + cross;
                cross = 0;
                if (sum > 9) {
                    sum -= 10;
                    cross = 1;
                }
                auto new_node = new ListNode(sum);
                new_node->next = cur->next;
                cur->next = new_node;
                s1.pop();
            }
        }

        if (cross == 1) {
            auto new_node = new ListNode(cross);
            new_node->next = cur->next;
            cur->next = new_node;
        }

        return fake.next;
    }
};