C++，用vector存储整个链表

        if (head == NULL || head->next == NULL || head->next->next == NULL)
            return;
        vector<ListNode *> v;
        while(head!=NULL){
            v.emplace_back(head);
            head=head->next;
        }
        int i=0,j=v.size()-1;
        while(i<j){
            v.at(i)->next=v.at(j);
            ++i;
            if(i==j)
                break;
            v.at(j)->next=v.at(i);
            --j;
        }
        v.at(i)->next=NULL;