Question

我需要根据此标头创建一个C ++队列（使用链接列表）：

class queue
{
  public:
    queue(); // constructor - constructs a new empty queue.
    void enqueue( int item ); // enqueues item.
    int dequeue();  // dequeues the front item.
    int front();   // returns the front item without dequeuing it.
    bool empty();  // true iff the queue contains no items.
    int size();  // the current number of items in the queue.
    int remove(int item); // removes all occurrances of item 
      // from the queue, returning the number removed.

  private:
    class node  // node type for the linked list 
    {
       public:
           node(int new_data, node * prev_node, node * next_node){
              data = new_data ;
              next = next_node ;
              prev = prev_node ;
           }
           int data ;
           node * next ;
           node * prev ;
    };

    node * front_p ;
    node * back_p ;
    int current_size ; // current number of elements in the queue.
};

这是我到目前为止所做的：

#include <iostream>
#include "queue.h"
using namespace std;

queue::queue(){

    current_size = 0;
    front_p = new node(NULL, NULL, NULL);
    back_p = new node(NULL, NULL, NULL);
}

void queue::enqueue(int item){

    if (current_size == 0){
        node * new_node;
        new_node = new node(item, back_p, front_p);
        front_p->prev = new_node;
        back_p->next = new_node;
        current_size = current_size + 1;
    }

    else if (current_size > 0){
        node * new_node;
        new_node = new node(item, back_p, back_p->next);
        back_p->next = new_node;
        new_node->next->prev = new_node;
        current_size = current_size + 1;
    }
}

int queue::dequeue(){

    if (current_size > 0) {

    node *remove = front_p->prev;

    return remove->data;

    remove-> prev->next = front_p;
    front_p->prev = remove->prev;

    delete remove;

    current_size = current_size - 1;
    }

    else if (current_size == 0) {
        return NULL;
    }

    else {
        return NULL;
    }
}

int queue::front(){

    return front_p -> prev -> data;
}

bool queue::empty(){

    return current_size == 0;
}

int queue::size(){

    return current_size;
}

int queue::remove(int item){

    for (int i = 0; i < current_size; i++){


    }
    return NULL;
}

int main(){

    int int1, int2;
    cout << "Welcome to the double linked list test program" << endl << "Please enter a #" << endl;
    cin >> int1;
    cout << "Another number" << endl;
    cin >> int2;

    queue * main_queue;
    main_queue = new queue();

    main_queue->enqueue(int1);
    main_queue->enqueue(int2);

    cout << "The front element is: " << main_queue->front() << endl;

    cout << "I have dequeued: " << main_queue->dequeue() << endl;

    cout << "The front element now: " << main_queue->front() << endl;

}

但是当我运行程序时，我得到相同的数字三次，表明它没有正确地出列？

Answer 1

这是你的问题：

if (current_size > 0) {
return front_p->data;
node * temp = front_p;
front_p = front_p->prev;
delete temp;
}

你在if语句中做的第一件事是从函数返回。在return之后，函数中不再执行任何代码。

Answer 2

我认为您需要将您的出列代码更改为这样。

 if(current_size > 0)
 {
   node *remove = front_p->prev;  
   remove-> prev->next = front_p;
   front_p->prev = remove->prev;      
   current_size = current_size - 1;
   return remove->data;  
 }

如上所述，您的return语句不允许在其下面执行任何其他代码。

为什么我的C ++队列没有正确出列？

2 个答案: