利用单链表实现电话本的模拟程序：定义单链表的数据类型，将头插法和尾插法、插入、删除、查找、修改、计数、逆置、输出等操作

定义单链表的数据类型：

struct ListNode {
    string name;
    string phone;
    ListNode* next;
};

头插法：

ListNode* head = nullptr;
void insertAtHead(string name, string phone) {
    ListNode* node = new ListNode{name, phone, nullptr};
    if (head == nullptr) {
        head = node;
    } else {
        node->next = head;
        head = node;
    }
}

尾插法：

ListNode* head = nullptr;
void insertAtTail(string name, string phone) {
    ListNode* node = new ListNode{name, phone, nullptr};
    if (head == nullptr) {
        head = node;
    } else {
        ListNode* tail = head;
        while (tail->next != nullptr) {
            tail = tail->next;
        }
        tail->next = node;
    }
}

插入：

void insert(string name, string phone, int index) {
    ListNode* node = new ListNode{name, phone, nullptr};
    if (index == 0) {
        insertAtHead(name, phone);
    } else {
        ListNode* prev = head;
        for (int i = 0; i < index - 1 && prev != nullptr; i++) {
            prev = prev->next;
        }
        if (prev != nullptr) {
            node->next = prev->next;
            prev->next = node;
        }
    }
}

删除：

void remove(string name) {
    ListNode* prev = nullptr;
    ListNode* curr = head;
    while (curr != nullptr && curr->name != name) {
        prev = curr;
        curr = curr->next;
    }
    if (curr != nullptr) {
        if (prev == nullptr) {
            head = curr->next;
        } else {
            prev->next = curr->next;
        }
        delete curr;
    }
}

查找：

ListNode* find(string name) {
    ListNode* curr = head;
    while (curr != nullptr && curr->name != name) {
        curr = curr->next;
    }
    return curr;
}

修改：

void update(string name, string newPhone) {
    ListNode* node = find(name);
    if (node != nullptr) {
        node->phone = newPhone;
    }
}

计数：

int count() {
    int cnt = 0;
    ListNode* curr = head;
    while (curr != nullptr) {
        cnt++;
        curr = curr->next;
    }
    return cnt;
}

逆置：

void reverse() {
    ListNode* prev = nullptr;
    ListNode* curr = head;
    while (curr != nullptr) {
        ListNode* next = curr->next;
        curr->next = prev;
        prev = curr;
        curr = next;
    }
    head = prev;
}

输出：

void print() {
    ListNode* curr = head;
    while (curr != nullptr) {
        cout << curr->name << ": " << curr->phone << endl;
        curr = curr->next;
    }
}