单向链表

#pragma once

// List.h

#include <iostream>

using namespace std;

struct Node
{
    int element;
    Node *next;
};

class List           //单向链表
{
public:
    List();
    bool empty() const;        //检查链表是否为空
    int front() const;        //返回链表的第一个元素
    int back() const;        //返回链表的最后一个元素
    int size() const;          //返回链表的长度
    Node* find(int ele);       //返回指向ele的指针
    void insert(int position, int ele);     //在position位置插入ele (head处于position = 0的位置)
    void push_back(int ele);                //在尾部插入
    void remove(int ele);               //删除值为ele的所有元素
    void clear();              //清空链表，有了这个操作之后就不要定义析构函数了
    void print();              //打印链表中的所有元素

private:
    Node *head;                //头结点
    int length;                //链表长度
};

List::List()
{
    head = new Node;        //head不能是nullptr，不然head->next是未定义的行为
    head->next = nullptr;
    length = 0;
}

bool List::empty() const
{
    return (head->next) == nullptr;
}

int List::front() const
{
    return (head->next)->element;
}

int List::back() const
{
    Node* p = head;
    while (p->next != nullptr)
        p = p->next;
    return p->element;
}

int List::size() const
{
    return length;
}


Node* List::find(int ele)
{
    Node* p = head;
    while (p->next != nullptr)
    {
        p = p->next;
        if (p->element = ele)
            return p;
    }
    cout << "Not find this element!" << endl;
    return nullptr;
}

void List::insert(int position, int ele)   //在特定位置插入元素,在position位置插入一个元素
{
    Node* p = head;
    for (int i = 1; i <= position - 1; ++i)
        p = p->next;   //获取position前一个位置的指针p
    Node *newNode = new Node;
    newNode->element = ele;
    newNode->next = p->next;
    p->next = newNode;
    ++length;
}

void List::push_back(int ele)
{
    Node* p = head;
    while (p->next != nullptr)
        p = p->next;
    Node *newNode = new Node;
    newNode->element = ele;
    p->next = newNode;
    newNode->next = nullptr;
    ++length;
}

void List::remove(int ele)
{
    Node *q = head;
    auto p = q->next;

    while (p != nullptr)
    {
        if (p->element == ele)
        {
            q->next = p->next;
            delete p;
            p = q->next;
            --length;
        }
        else
        {
            q = p;
            p = q->next;
        }
    }
}

void List::clear()
{
    Node* p1 = head->next;
    while (p1 != nullptr)
    {
        auto p2 = p1->next;
        delete p1;
        if (p2 != nullptr)
            p1 = p2;
        else break;
    }
    length = 0;
}

void List::print()
{
    Node* p1 = head->next;
    while (p1 != nullptr)
    {
        cout << p1->element << ' ';
        p1 = p1->next;
    }
}

//main.cpp

#include <iostream>
#include "List.h"

using namespace std;

int main()
{
    List lst;
    lst.push_back(1);
    lst.push_back(2);
    lst.push_back(3);
    lst.push_back(2);
    lst.push_back(9);
    lst.remove(2);

    cout << lst.size();


    return 0;
}