假设 head != nullptr，下面是实现单向循环链表在头节点后插入新节点的代码，横线处应填入（ ）。
head != nullptr
struct Node { int val; Node* next; }; void insertAfterHead(Node* head, int x) { Node* newNode = new Node; newNode->val = x; ______________________ // 在此处填入代码 }
newNode->next = head; head->next = newNode;
newNode->next = head->next; head->next = newNode;
head->next = newNode; newNode->next = head->next;
newNode->next = head->next; head = newNode;