一直segmentfault的代码

class Solution {
public:
    ListNode *copyRandomList(ListNode *head) {
         ListNode* new_head = new ListNode(-1);
         new_head->next = head;
         ListNode* p = new_head->next;
        while(p) {
            ListNode* q = new ListNode(p->val);
            q->next = p->next;
            p->next = q;
            p = q->next;
        }
        p = new_head->next;
        //第18行导致segmentfault，原因是p可能是空啊，
        new_head->next = p->next;
        while(p) {
            if(p->random) {
                p->next->random = p->random->next;
            }
            ListNode* res = p->next->next;
            p = res;
        }
        // return new_head->next;


        // for (auto p = head; p; p = p->next->next)
        // {
        //     if (p->random)
        //         p->next->random = p->random->next;
        // }

        auto dummy = new ListNode(-1);
        auto cur = dummy;
        for (auto p = head; p; p = p->next)
        {
            cur->next = p->next;
            cur = cur->next;
            p->next = p->next->next;
        }
        return dummy->next;
    }
};