我正在尝试删除C ++中的重复项。我已经设法通过使用对象默认构造函数将对象设置为= null。但我无法将其从列表中完全删除。此代码还删除了两个对象而不是一个。这是另一个问题的重新发布。我的代码和部分帖子已更改。How to remove duplicates from a doubly linked list by full name。谁能帮我这个？这是我的removeDuplicates函数：
***Remove Duplicates***
void RemoveDuplicates(DoublyLinkedListIterator<Datatype> m_itr, string searchByFirstName, string searchBySecondName)
{
for (m_itr.Start(); m_itr.Valid(); m_itr.Forth())
{
if ((m_itr.Item().getFirstName() == searchByFirstName )
&& (m_itr.Item().getSecondName() == searchBySecondName))
{
for (m_itr.Item(); m_itr.Valid(); m_itr.Forth())
{
if ((m_itr.Item().getFirstName() == searchByFirstName )&&
(m_itr.Item().getSecondName() == searchBySecondName))
{
m_itr.Item() = Stats();
}
}
}
}
delete m_itr.Item();
}
***Remove***
void Remove(DoublyLinkedListIterator<Datatype> m_itr)
{
query.clock1();
DoublyLinkedListNode<Datatype>* node = m_head;
//Check to see if the iterator belongs to this list, if not return nothing.
if (m_itr.m_list != this)
return;
//Check to see if the node is valid, if not return nothing.
if (m_itr.m_node == 0)
return;
//If the iterator is pointing to the head...
if (m_itr.m_node == m_head)
{
//Move the iterator forward.
m_itr.Forth();
//Delete the head.
RemoveHead();
//Decrement the size.
m_count--;
}
//If the iterator is not pointing to the head...
else
{
//Search forward through the list until you find
//the node prior to the node you want to remove.
while (node->m_next != m_itr.m_node)
node = node->m_next;
// move the iterator forward.
m_itr.Forth();
//If the node being are deleted is the tail...
//Then update the tail node.
if (node->m_next == m_tail)
{
//Tail is now equal to node. Which means we can now delete the node.
m_tail = node;
}
//Delete the node.
delete node -> m_next;
//Relink the list.
node -> m_next = m_itr.m_node;
//Decrement the count because a node was removed.
m_count--;
query.clock2();
cout << "\nTime Taken : " << query.time2 - query.time1 << "\n";
}
}
***Class Declarations***
template <class Datatype>
class DoublyLinkedList
{
public:
//-------------------------------------------------------------------------------------------
// Member Vairables.
//-------------------------------------------------------------------------------------------
DoublyLinkedListNode<Datatype>* m_head;
DoublyLinkedListNode<Datatype>* m_tail;
int m_count;
template<class Datatype>
class DoublyLinkedListNode
{
public:
//-------------------------------------------------------------------------------------------
// Member Vairables.
//-------------------------------------------------------------------------------------------
DoublyLinkedListNode<Datatype>* m_next; //The next node.
DoublyLinkedListNode<Datatype>* m_prev; //The previous node.
Datatype m_data; //The data in the node.
template <class Datatype>
class DoublyLinkedListIterator
{
public:
//-------------------------------------------------------------------------------------------
// Member Vairables.
//-------------------------------------------------------------------------------------------
DoublyLinkedListNode<Datatype>* m_node; //A node for the Iterator to pointn to.
DoublyLinkedList<Datatype>* m_list; //A list for the Iteraotor to go through.
//-------------------------------------------------------------------------------------------
// Name: Constructor.
// Description: Constructs the DoublyLinkedListIterator.
//-------------------------------------------------------------------------------------------
DoublyLinkedListIterator(DoublyLinkedList<Datatype>* p_list= 0, DoublyLinkedListNode<Datatype>* p_node= 0)
{
m_list= p_list;
m_node= p_node;
}
// ------------------------------------------------------------------
// Name: Start
// Description: Resets the iterator to the beginning of the list.
// Arguments: None.
// Return Value: None.
// ------------------------------------------------------------------
void Start()
{
if(m_list!= 0)
m_node= m_list -> m_head;
}
// ----------------------------------------------------------------
// Name: End
// Description: Resets the iterator to the end of the list.
// Arguments: None.
// Return Value: None.
// ----------------------------------------------------------------
void End()
{
if(m_list!= 0)
m_node = m_list->m_tail;
}
// ----------------------------------------------------------------
// Name: Forth
// Description: Moves the iterator forward by one position.
// Arguments: None.
// Return Value: None.
// ----------------------------------------------------------------
void Forth()
{
if(m_node != 0)
{
m_node = m_node ->m_next;
}
}
// ----------------------------------------------------------------
// Name: Back
// Description: Moves the iterator back by one position.
// Arguments: None.
// Return Value: None.
// ----------------------------------------------------------------
void Back()
{
if(m_node!= 0)
m_node = m_node->m_prev;
}
// ----------------------------------------------------------------
// Name: Item
// Description: Gets the item that the iterator is pointing to.
// Arguments: None.
// Return Value: Reference to the data in the node.
// ----------------------------------------------------------------
Datatype& Item()
{
return m_node->m_data;
}
//-----------------------------------------------------------------
// Name: Valid
// Description: Determines if the node is valid.
// Arguments: None.
// Return Value: true if valid.
// ----------------------------------------------------------------
bool Valid()
{
return (m_node!= 0);
}
};
答案 0 :(得分：2)
使用DoublyLinkedList的内置Remove函数并将其传递给迭代器。 删除调用是基本的C ++变体，它不处理节点删除和正确重新链接列表。对删除的调用只会删除节点中的内容，而不会删除节点本身！
Remove(m_itr);
而不是
delete m_itr.Item();
另外，我认为您删除的地方可能已关闭（您似乎总是删除最后一项，似乎）。也许你想做类似下面的事情。不确定Stats（）做了什么，但希望你能得到这个想法。基本上你需要放弃要删除的项目，向前移动常规迭代器，然后删除你放的那个。或者，一旦删除完成，完全停止迭代。这是必需的，因为当迭代器被删除时，它不能用于进一步的迭代。
if ((m_itr.Item().getFirstName() == searchByFirstName ) &&
(m_itr.Item().getSecondName() == searchBySecondName))
{
DoublyLinkedListIterator<Datatype> toDelete = m_itr;
m_itr.Forth();
Remove(toDelete);
}
答案 1 :(得分：2)
内部for循环没有为你做任何事情：它只是继续外循环开始的迭代。
这里有很多问题，我猜你正在学习，我赞赏你的努力：有利于你伸出援手。
void RemoveDuplicates(DoublyLinkedListIterator<Datatype> m_itr, string searchByFirstName, string searchBySecondName)
{
for (m_itr.Start(); m_itr.Valid(); m_itr.Forth())
{
if ((m_itr.Item().getFirstName() == searchByFirstName )&& (m_itr.Item().getSecondName() == searchBySecondName))
{
if ((m_itr.Item().getFirstName() == searchByFirstName )&&
(m_itr.Item().getSecondName() == searchBySecondName))
{
m_itr.Item() = Stats();
}
}
}
delete m_itr.Item();
}
将项目分配给统计数据也可能不是您想要的：您想要删除该项目，然后从列表中删除该项目。我需要看到迭代器和双向链表的api，但你需要删除该项，并将其从列表中删除，可能涉及到这样的内容：
m_itr.Item().m_prev.m_next = m_itr.Item().m_next;
if (m_itr.Item().m_next != null)
m_itr.Item().m_next.m_prev = m_itr.Item().m_prev;
// now that the item is spliced out of the list, delete it.
希望这有帮助。
答案 2 :(得分：1)
我对您正在使用的库一无所知，但在标准库中，删除时请执行以下操作：
for (auto i = begin(list); i != end(list);) {
if (dont_want(*i)) {
i = list.erase(i);
} else {
++i;
}
}
基本思想是，在循环内部，要么是要擦除当前节点，要么是list.erase(…)以告知您哪个节点在擦除当前节点后继续迭代，或者你保持节点，在这种情况下，你只需通过递增迭代器就可以移动它。
在您的代码中，++i的等效值为m_itr.Forth()，而list.erase(…)为Remove(…)。但是，由于Remove()没有返回有关如何继续进行列表的任何信息，因此您会陷入困境;您无法调用m_itr.Forth()，因为它指向的节点不再存在。
我不知道我可以为你提供更多帮助，因为我很难理解你的代码是如何工作的。表达式m_itr.Item().getFirstName()表示m_itr.Item()是对象的引用，而delete m_itr.Item()表示它必须是指针，而不是引用。
请注意，上面的代码符合C ++ 11。 C ++ 03的等价物是：
for (std::list<Datatype>::iterator i = list.begin(); i != list.end();) { … }