DList

#include<iostream>
using namespace std;
typedef int DataType;
class LinkNode
{
public:
	LinkNode(const DataType &x)
		:_data(x)
		, _prev(NULL)
		, _next(NULL)
	{}
	friend class DList;
private:
	DataType _data;
	LinkNode *_prev;
	LinkNode *_next;
};

class DList
{
public:
	DList()
		:_head(NULL)
		, _tail(NULL)
	{}
public:
	void Print()
	{
		if (_head == NULL)
		{
			return;
		}
		LinkNode *begin = _head;
		cout << "DList->";
		while (begin)
		{
			cout << begin->_data << "->";
			begin = begin->_next;
		}
		cout << endl;
	}
	void PushBack(const DataType &x)
	{
		if (_head == NULL)
		{
			_head = new LinkNode(x);
			_tail = _head;
			return;
		}
		_tail->_next = new LinkNode(x);
		_tail->_next->_prev = _tail;
		_tail = _tail->_next;
	}
	void PushFront(const DataType &x)
	{
		if (_head == NULL)
		{
			_head = new LinkNode(x);
			_tail = _head;
			return;
		}
		_head->_prev = new LinkNode(x);
		_head->_prev->_next = _head;
		_head = _head->_prev;
	}
	void PopBack()
	{
		if (_head == NULL)
		{
			return;
		}
		if (_head == _tail)
		{
			delete _head;
			_head = NULL;
			_tail = NULL;
			return;
		}
		_tail->_prev->_next = NULL;
		LinkNode *del = _tail;
		_tail = _tail->_prev;
		delete del;
	}
	void PopFront()
	{
		if (_head == NULL)
		{
			return;
		}
		if (_head == _tail)
		{
			delete _head;
			_head = NULL;
			_tail = NULL;
			return;
		}
		LinkNode *del = _head;
		_head = _head->_next;
		delete del;
	}
	LinkNode *Find(const DataType &x)
	{
		LinkNode *begin = _head;
		if (_head == NULL)
		{
			return NULL;
		}
		while (begin)
		{
			if (begin->_data == x)
			{
				return begin;
			}
			begin = begin->_next;
		}
		return NULL;
	}
	void Insert(LinkNode *n, const DataType &x)
	{
		//1.空链表
		if (_head == NULL)
		{
			return;
		}
		//2.插到尾结点之后
		if (n == _tail)
		{
			_tail = new LinkNode(x);
			n->_next = _tail;
			_tail->_prev = n;
			return;
		}
		//3.插到中间某个结点之后
		LinkNode *tmp = new LinkNode(x);
		tmp->_next = n->_next;
		n->_next->_prev = tmp;
		n->_next = tmp;
		tmp->_prev = n;
	}
	void Erase(LinkNode *del)
	{
		//1.空表
		if (_head == NULL)
		{
			return;
		}
		//2.只有一个结点
		if (_head == _tail)
		{
			delete _head;
			_head = NULL;
			_tail = NULL;
			return;
		}
		//3.删除头结点
		if (_head == del)
		{
			_head = _head->_next;
			delete del;
			_head->_prev = NULL;
			return;
		}
		//4.删除尾结点
		if (del == _tail)
		{
			_tail = _tail->_prev;
			delete del;
			_tail->_next = NULL;
			return;
		}
		//5.删除中间结点
		del->_prev->_next = del->_next;
		del->_next->_prev = del->_prev;
		delete del;
	}
private:
	LinkNode *_head;
	LinkNode *_tail;
};