0001 template <typename T> void List<T>::reverse() { //前后倒置
0002    if (_size < 2) return; //平凡情况
0003    LNP<T> p, q;
0004    for (p = head, q = p->succ; p != tail; p = q, q = p->succ)
0005       p->pred = q; //自前向后，依次颠倒各节点的前驱指针
0006    tail->pred = nullptr; //单独设置尾节点的前驱指针
0007    for (p = head, q = p->pred; p != tail; p = q, q = p->pred)
0008       q->succ = p; //自前向后，依次颠倒各节点的后继指针
0009    head->succ = nullptr; //单独设置头节点的后继指针
0010    swap(head, tail); //头、尾节点互换
0011 } //reverse()