c++ 雙向鏈表

dList.h

#pragma once

#include <iostream>
#include <assert.h>
using namespace std;

typedef int DataType;

struct ListNode
{
    ListNode(DataType d = 0, ListNode* next = NULL, ListNode* prev = NULL)
        :_next(next), _prev(prev), _data(d)
    {}

    ListNode* _next;
    ListNode* _prev;
    DataType _data;
};

inline void Swap(ListNode*& pn1, ListNode*& pn2)
{
    ListNode* tmp = pn1;
    pn1 = pn2;
    pn2 = tmp;
}

class List
{
    typedef ListNode Node;
public:
    List()
        :_head(NULL), _tail(NULL)
    {}

    List(const List& l)
    {
        if (l._head == NULL)
        {
            List();
            return;
        }
        if (l._head == l._tail)//只有一個節點
        {
            _head = _tail = new Node(l._head->_data);
            if (l._head->_next != NULL)//帶環
                _head->_next = _head->_prev = _head;
        }

        Node* cur = _head = new Node(l._head->_data);
        Node* l_cur = l._head->_next;
        while (l_cur != l._tail)//cur 比 l_cur 慢一步，cur->next 複製的是 l_cur;
        {
            cur->_next = new Node(l_cur->_data, NULL, cur);
            cur = cur->_next;
            l_cur = l_cur->_next;
        }
        cur->_next = new Node(l_cur->_data, NULL, cur);

        //處理 環
        if (l._tail->_next != NULL)
        {
            if (l._tail->_next == l._head)
            {
                _tail->_next = _head;
                _head->_prev = _tail;
            }
            else
            {
                l_cur = l._head;
                cur = _head;
                while (l_cur != l._tail->_next)
                {
                    l_cur = l_cur->_next;
                    cur = cur->_next;
                }
                _tail->_next = cur;
            }
        }
    }

    List& operator=(const List& l)
    {
        List newlist(l);
        Swap(newlist);
        return *this;
    }

    ~List()
    {
        while (_head != _tail)
        {
            Node* tmp = _head;
            _head = _head->_next;
            delete tmp;
        }
        delete _tail;
    }

    void PushBack(DataType x)
    {
        if (_tail != NULL)
        {
            //Node* next = _tail->_next;
            //_tail->_next = new Node(x, _tail->_next, _tail);
            //_tail = next;

            _tail->_next = new Node(x, _tail->_next, _tail);
            _tail = _tail->_next;
        }
        else//空鏈表
            _tail = _head = new Node(x);
    }

    void PopBack()
    {
        if (_tail = NULL)
            return;
        Node* oldTail = _tail;
        _tail = _tail->_prev;
        _tail->_next = oldTail->_next;
        delete oldTail;
    }

    void PushFront(DataType x)
    {
        if (_head == NULL)
            _head = _tail = new Node(x);
        else
        {
            _head->_prev = new Node(x, _head, _head->_prev);
            _head = _head->_prev;
        }
    }

    void PopFront()
    {
        if (_head = NULL)
            return;
        Node* oldHead = _head;
        _head = _head->_next;
        _head->_prev = oldHead->_prev;
        delete oldHead;
    }

        // 在pos的前面插入一個 
    void Insert(Node* pos, DataType x)
    {
        assert(pos);

        pos->_prev = pos->_prev->_next = new Node(x, pos, pos->_prev);
    }

    void Erase(Node* pos)
    {
        pos->_prev->_next = pos->_next;
        pos->_next->_prev = pos->_prev;
        delete pos;//可以不寫
    }

    Node* Find(DataType x)
    {
        Node* ret = _head;
        while (ret->_data != x && ret != _tail)
        {
            ret = ret->_next;
        }
        if (ret->_data == x)
            return ret;
        return _tail->_data == x ? _tail : NULL;
    }

    void Reverse()
    {
        if (_head == NULL || _head == _tail)
            return;

        Node* cur = _head;
        while (cur != _tail)
        {
            ::Swap(cur->_next, cur->_prev);
            cur = cur->_prev;
        }
        ::Swap(cur->_next, cur->_prev);
        ::Swap(_tail, _head);
    }

    void Swap(List& l)
    {
        ::Swap(_head, l._head);
        ::Swap(_tail, l._tail);
    }

private:
    Node* _head;
    Node* _tail;
};