链表

手写双链表：

#include <iostream>
 
// 链表节点结构体
struct ListNode {
    int value;
    ListNode* prev;
    ListNode* next;
 
    ListNode(int v, ListNode* p = nullptr, ListNode* n = nullptr) : value(v), prev(p), next(n) {}
};
 
class LinkedList {
public:
    LinkedList() : head(nullptr), tail(nullptr), size(0) {}
    ~LinkedList() { clear(); }
 
    // 在链表末尾添加元素
    void push_back(int value) {
        if (size == 0) {
            head = tail = new ListNode(value);
        } else {
            tail->next = new ListNode(value, tail);
            tail = tail->next;
        }
        ++size;
    }
 
    // 删除链表末尾元素
    void pop_back() {
        if (size == 0) return;
        ListNode* temp = tail;
        if (size == 1) {
            head = tail = nullptr;
        } else {
            tail = tail->prev;
            tail->next = nullptr;
        }
        delete temp;
        --size;
    }

    // 在指定位置插入节点
    void insert(int index, int value) {
        if (index < 0 || index > size) {
            std::cout << "Invalid index" << std::endl;
            return;
        }
        if (index == 0) {
            head = new ListNode(value, nullptr, head);
            if (size == 0) {
                tail = head;
            } else {
                head->next->prev = head;
            }
        } else if (index == size) {
            push_back(value);
        } else {
            ListNode* current = head;
            for (int i = 0; i < index - 1; ++i) {
                current = current->next;
            }
            current->next = new ListNode(value, current, current->next);
            current->next->next->prev = current->next;
        }
        ++size;
    }

    // 删除指定位置的节点
    void erase(int index) {
        if (index < 0 || index >= size) {
            std::cout << "Invalid index" << std::endl;
            return;
        }
        if (index == 0) {
            ListNode* temp = head;
            head = head->next;
            if (head) {
                head->prev = nullptr;
            } else {
                tail = nullptr;
            }
            delete temp;
        } else if (index == size - 1) {
            pop_back();
        } else {
            ListNode* current = head;
            for (int i = 0; i < index; ++i) {
                current = current->next;
            }
            current->prev->next = current->next;
            current->next->prev = current->prev;
            delete current;
        }
        --size;
    }
 
    // 清空链表
    void clear() {
        while (size > 0) {
            pop_back();
        }
    }
 
    // 获取链表长度
    int get_size() const { return size; }
 
    // 打印链表元素
    void print() const {
        ListNode* temp = head;
        while (temp) {
            std::cout << temp->value << " ";
            temp = temp->next;
        }
        std::cout << std::endl;
    }
 
private:
    ListNode* head;
    ListNode* tail;
    int size;
};
 
int main() {
    LinkedList list;
    list.push_back(1);
    list.push_back(2);
    list.push_back(3);
    list.push_back(4);
    list.push_back(5);
 
    std::cout << "List: ";
    list.print();
    std::cout << "Size: " << list.get_size() << std::endl;
 
    list.pop_back();
    std::cout << "List after pop_back: ";
    list.print();
    std::cout << "Size: " << list.get_size() << std::endl;
 
    return 0;
}