面对链表队列的问题 [英] Facing problem with linked list queue

问题描述

你好!!我在我的代码中面临的问题基本上我正在使用队列技术+使用模板实现链接列表，但问题在于，当我实现浮点数和字符串类型时，它显示了我完美的答案，但它不适用于int类型我我在这里写入入队和出队功能以获得通关!!



我尝试了什么：

 #include< iostream> 
 #include< string> 
 using namespace std; 
 
模板< typename类型> 
 struct Node 
 {
类型信息; 
节点<类型> *下一个; 
}; 
模板< typename类型> 
 void Queue< Type> :: Enqueue（Type x）
 {
 Node< Type> *温度; 
 temp = new Node< Type> ;; 
 temp-> info = x; 
 temp-> Next = NULL; 
 if（front == NULL）
 {
 front = temp; 
} 
 else 
 {
 rear-> Next = temp; 
} 
 
 rear = temp; 
 
} 

模板< typename类型> 
 void Queue< Type> :: Dequeue（）
 {
 Node< Type> *温度; 
 temp = new Node< Type> ;; 
 
 if（front == NULL）
 {
 cout<< 队列是空的。<< ENDL; 
} 
其他
 {
 temp = front; 
 front = front-> Next; 
 cout<< endl<< temp-> info<< 已经出局了。 << ENDL; 
删除临时; 
} 
} 

 int main（）
 {
 
 cout<< ============== Int Queue ==============<< ENDL; 
 Queue< int> intqueue; 
 intqueue.Enqueue（20）; 
 intqueue.Enqueue（30）; 
 intqueue.Enqueue（40）; 
 intqueue.Print（）; 
 intqueue.Dequeue（）; 
 intqueue.Print（）;} 

解决方案

我将通过在您的代码中添加注释来回答：

模板< typename类型> 
 void Queue< Type> :: Dequeue（）
 {
 Node< Type> *温度; 
 //永远不会删除此处创建的实例：内存泄漏。 
 //只需删除此行即可。 
 temp = new Node< Type> ;; 
 
 if（front == NULL）
 {
 cout<< 队列是空的。<< ENDL; 
} 
其他
 {
 //你在这里删除前面。 
 //删除示例会话中的20。 
 //如果你想删除最后一项，你应该使用后方：
 // temp = rear; 
 // rear = rear-> Prev; 
 //后 - >下一个= NULL; 
 temp = front; 
 front = front-> Next; 
 cout<< endl<< temp-> info<< 已经出局了。 << ENDL; 
删除临时; 
} 
} 

如果您使用调试器，您很快就会看到错误。你真的应该熟悉它。



我在你的代码中看到的是你没有更新前面和后方。例如：后面指向空队列的是什么？可能是NULL，我假设。那么在插入第一个元素时， Enqueue 会发生什么？您正在使用读取指针（为空）并执行：

 rear-> Next = temp ; 

将产生未定义的结果。同样在 Dequeue 中：当你删除最后一个元素时会发生什么？在这种情况下，前和后应设置为NULL。我在你的代码中没有看到。所以你再次引发了未定义的行为。




hello !! i am facing little problem here in my code basically i am implementing linked list using queue technique + using templates but the problem in that is when i implement float and string types it shows me perfect answer but it is not working for "int" type i am writing enqueue and dequeue functions here for clearance !!

What I have tried:



#include <iostream>
#include <string>
using namespace std;

template <typename Type>
struct Node
{
	Type info;
	Node<Type> *Next;
};
template <typename Type>
void Queue<Type>::Enqueue(Type x)
{
	Node<Type> *temp;
	temp = new Node<Type>;
	temp->info = x;
	temp->Next = NULL;
	if (front == NULL)
	{
		front = temp;
	}
	else
	{
		rear->Next = temp;
	}

	rear = temp;

}





template <typename Type>
void Queue<Type>::Dequeue()
{
	Node<Type> *temp;
	temp = new Node<Type>;

	if (front == NULL)
	{
		cout << " Queue is Empty. " << endl;
	}
	else
	{
		temp = front;
		front = front->Next;
		cout << endl << temp->info << " was dequeued." << endl;
		delete temp;
	}
}





int main()
{

	cout << "============== Int Queue ==============" << endl;
	Queue<int>intqueue;
	intqueue.Enqueue(20);
	intqueue.Enqueue(30);
	intqueue.Enqueue(40);
	intqueue.Print();
	intqueue.Dequeue();
	intqueue.Print();}

解决方案

I will answer by adding comments to your code:

template <typename Type>
void Queue<Type>::Dequeue()
{
    Node<Type> *temp;
    // The instance created here is never deleted: Memory leak.
    // Just remove this line.
    temp = new Node<Type>;

    if (front == NULL)
    {
        cout << " Queue is Empty. " << endl;
    }
    else
    {
        // You are removing the front here.
        // So 20 from your example session is removed.
        // If you want to remove the last item you should use rear instead:
        //  temp = rear;
        //  rear = rear->Prev;
        //  rear->Next = NULL;
        temp = front;
        front = front->Next;
        cout << endl << temp->info << " was dequeued." << endl;
        delete temp;
    }
}




If you would use the debugger you would quickly see what's wrong. You should really get acquainted to use it.

What I can see in your code is that you don't update front and rear consequently. For example: What does rear point to in an empty queue? Probably NULL, I assume. So what happens in Enqueue when you are inserting the first element? You are using the read pointer (which is null) and do:

rear->Next = temp;

which will produce undefined results. Similarly in Dequeue: What happens when you remove the last element? In that case front and rear should be set to NULL. I don't see that in your code. So again you are provoking undefined behavior.




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