双链表操作（不带头结点）

struct Node {
    int val;
    struct Node* prior, *next;
    Node(int v) : val(v) { prior = NULL; next = NULL; }
};

构建双链表

struct Node* build() {
    struct Node* head = NULL;
    struct Node* ptr = NULL;
    int val; 
    while (cin >> val) {
        if (head == NULL) {
            head = new Node(val);
            head->next = head;
            ptr = head;
        }
        else {
            ptr->next = new Node(val);
            ptr->next->prior = ptr;
            ptr = ptr->next;
        }
    }
    if (head != NULL) {
        head->prior = ptr;
        ptr->next = head;
    }
    return head; 
}

遍历

//升序遍历
void ascendingTraverse(struct Node* head) {
    if (head == NULL)
        return;
    auto ptr = head;
    do {
        cout << ptr->val;
        ptr = ptr->next;
        if (ptr == head) {
            cout << endl;
        }
        else {
            cout << " ";
        }
    } while (ptr != head);
}
// 逆序遍历
void descendingTraverse(struct Node* head) {
    if (head == NULL)
        return;
    auto ptr = head->prior;
    do {
        cout << ptr->val;
        ptr = ptr->prior;
        if (ptr == head->prior) {
            cout << endl;
        }
        else {
            cout << " ";
        }
    } while (ptr != head->prior);
}

插入排序 重点

/*移动结点内的元素，而不是结点本身*/
/*注意head会发生变化*/
void sort(struct Node*& head) { 
    if (!head)
        return;
    for (auto ptr = head->next; ptr != head; ptr = ptr->next) {
        int tmp = ptr->val; 
        struct Node* pri;
        /* 注意该条件：pri != head->prior */
        for (pri = ptr->prior; pri != head->prior && pri->val > tmp ; pri = pri->prior){
            pri->next->val = pri->val; 
        }
        pri->next->val = tmp; 
    }
    int minNum = head->val;
    auto newHead = head; 
    for (auto ptr = head->next; ptr != head; ptr = ptr->next) {
        if (minNum > ptr->val) {
            newHead = ptr;
            minNum = ptr->val;
        }
    }
    head = newHead; 
}

删除

void destroy(struct Node* head) {
    if (!head)
        return;
    for (auto ptr = head->next; ptr != head; ) {
        auto tmp = ptr->next;
        delete ptr;
        ptr = tmp; 
    }
    delete head;
}