单链表简单实现

用作复习，简单实现下单链表，这里我自己添加了个尾指针。

#include<iostream>using namespace std;template<class T>struct Node{    T _val;    Node<T>* _next;    Node(const T& val)        :_val(val)        ,_next(NULL)    {}};template<class T>class List{    typedef Node<T> Node;public:    List<T>();    ~List();    List(const List& l);    List& operator=(const List& l);    void push_back(const T& val);    void pop_back();    pair<Node*,bool> find(const T& val);    bool Delete(const T& val);public:    Node* BuyNode(const T& val);    void erase();private:    Node* head;    Node* tail;};template<class T>List<T>::List()    : head(new Node(0))    , tail(head){}template<class T>List<T>::~List(){}template<class T>List<T>::List(const List<T>& l):head(new Node(0)){    Node* cur = l.head->_next;    Node* tmp = head;    while (cur){        tmp->_next = BuyNode(cur->_val);        tmp = tmp->_next;        cur = cur->_next;    }}template<class T>List<T>& List<T>::operator=(const List<T>& l){    if (this != &l){        erase();        head = new Node(0);        tail = head;        Node* cur = l.head->_next;        Node* tmp = head;        while (cur){            tail->_next = BuyNode(cur->_val);            tail = tail->_next;            cur = cur->_next;        }    }    return *this;}template<class T>void List<T>::push_back(const T& val){    tail->_next = BuyNode(val);    tail = tail->_next;}template<class T>void List<T>::pop_back(){    Node* cur = head;    if (head==tail)        return;    while (cur->_next != tail){        cur = cur->_next;    }    delete tail;    tail = cur;    tail->_next = NULL;}template<class T>pair<Node<T>*,bool> List<T>::find(const T& val){    Node* cur = head;    while (cur->_next && cur->_next->_val!=val){        cur = cur->_next;    }    if (cur->_next)        return make_pair(cur, true);    return make_pair(cur, false);}template<class T>bool List<T>::Delete(const T& val){    Node* tmp = find(val).first;    if (tmp->_next == NULL)        return false;    Node* del = tmp->_next;    if (del == tail)        tail = tmp;    tmp->_next = del->_next;    delete del;    return true;}template<class T>Node<T>* List<T>::BuyNode(const T& val){    return new Node(val);}template<class T>void List<T>::erase(){    while (head)    {        Node* del = head;        head = head->_next;        delete del;    }}