题解 | 链式A+B

/*
struct ListNode {
    int val;
    struct ListNode *next;
    ListNode(int x) : val(x), next(NULL) {}
};*/
class Plus {
  public:
    ListNode* plusAB(ListNode* a, ListNode* b) {
        // write code here
        if (!a ) return b;
        if (!b) return a;
        auto* sum = new ListNode{0};
        ListNode* sptr = sum;
        bool over_flag = false;
        auto pa=a;
        auto pb=b;
        while (pa || pb) {
            int tmp_a = pa ? pa->val : 0;
            int tmp_b = pb ? pb->val : 0;

            int tmp = tmp_a + tmp_b + static_cast<int>(over_flag);
            over_flag = tmp > 9;
            auto s = new ListNode(tmp % 10);
            sptr->next = s;
            sptr = sptr->next;
            if(pa)pa = pa->next;
            if(pb)pb = pb->next;

        }
        if(over_flag){
            sptr->next = new ListNode(1);
        }
        return sum->next;

    }
};