C++实现双向链表

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#pragma once

typedef int DataType;
struct ListNode
{
ListNode* _next;
ListNode* _prev;
DataType _data;

ListNode(const DataType& x)
  :_data(x)
  ,_next(NULL)
  ,_prev(NULL)
{}
};

class List
{
typedef ListNode Node;
public:
List()
  :_head(NULL)
  ,_tail(NULL)
{}
List(const List& l)
  :_head(NULL)
  ,_tail(NULL)
{
  Node* cur = l._head;
  while (cur)
  {
   PushBack(cur->_data);
   cur = cur->_next;
  }
}

List& operator=(List l)
{
swap(_head, l._head);
swap(_tail, l._tail);
}

void Clear()
{
  Node* cur = _head;
  while (cur)
  {
   Node* next = cur->_next;
   delete cur;
   cur = next;
  }

_head = _tail = NULL;
}

~List()
{
Clear();
}

void PushBack(const DataType& x)
{
  if (_tail == NULL)
  {
   _head = _tail = new Node(x);
  }
  else
  {
   Node* tmp = new Node(x);
   _tail->_next = tmp;
   tmp->_prev = _tail;

_tail = tmp;
}
}

void PopBack()
{
Erase(_tail);
}

void PushFront(const DataType& x)
{
Insert(_head, x);
}

void PopFront()
{
  Erase(_head);
}
void Insert(Node* pos, const DataType& x)
{
  Node* tmp = new Node(x);
  if (_head == pos)
  {
   if(_head == NULL)
   {
    _head = _tail = tmp;
   }
   else
   {
    tmp->_next = _head;
    _head->_prev = tmp;
    _head = tmp;
   }
  }
  else
  {
   Node* prev = pos->_prev;
   prev->_next = tmp;
   tmp->_prev = prev;

   tmp->_next = pos;
   pos->_prev = tmp;
  }
}

void Erase(Node* pos)
{
  if (_head == _tail)
  {
   assert(_head == pos);
   _head = _tail = NULL;
  }
  else if (pos == _head)
  {
   _head = _head->_next;
   _head->_prev = NULL;
  }
  else if (pos == _tail)
  {
   _tail = _tail->_prev;
   _tail->_next = NULL;
  }
  else
  {
   Node* prev = pos->_prev;
   Node* next = pos->_next;
   prev->_next = next;
   next->_prev = prev;
  }

delete pos;
}

Node* Find(const DataType& x)
{
  Node* cur = _head;
  while (cur)
  {
   if (cur->_data == x)
   {
    return cur;
   }

cur = cur->_next;
}

return NULL;
}

void Print()
{
  Node* cur = _head;
  while (cur)
  {
   cout<<cur->_data<<" ";
   cur = cur->_next;
  }
  cout<<endl;
}

void Reverse()
{
  Node* cur = _head;
  while(cur)
  {
   swap(cur->_next, cur->_prev);
   cur = cur->_prev;
  }

swap(_head, _tail);
}

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

void TestList()
{
List l1;
l1.PushBack(1);
l1.PushBack(2);
l1.PushBack(3);
l1.PushBack(4);
l1.Print();

ListNode* pos = l1.Find(3);
l1.Insert(pos, 30);
pos = l1.Find(3);
l1.Erase(pos);
l1.Print();

l1.PopBack();
l1.PopBack();
l1.PopBack();
l1.PopBack();
l1.Print();
}

void TestList1()
{
List l1;
l1.PushBack(1);
l1.PushBack(2);
l1.PushBack(3);
l1.PushBack(4);
l1.Print();