[英]C++ Priority Queue Class with Linked List
我的C ++代碼有兩個問題(下面是測試文件):
我似乎無法弄清為什么它沒有退出while循環,而在運行時卻卡在了“ 7 vs 325”循環中。
因此,它應該進入temp的下一個節點(該節點為null),然后跳轉到將其添加到隊列末尾的部分。 但它只是循環而已。
我的第二個問題是我注釋掉的函數queue1.back,只要運行該函數,它就會出錯並給出看起來是地址的地址,但是.front()函數可以正常工作。
我正在使用的測試文件是這樣的:
89 Alex
325 Rob
72 Joy
91 Bob
using namespace std;
class Person
{
friend class Pqueue;
public:
int priority;
string name;
};
class PQueue
{
friend class Person;
private:
//Structure for my linked list.
typedef struct node {
Person data;
struct node *next;
}Node, *NodePtr;
Node *head, *tail;
public:
//Prototype Functions
PQueue(void); //Initializer function
bool empty(void); //Test if empty
int size(void); //Return size
void enqueue(Person *); //Insert Node
void dequeue(void); //Remove Node
Person* front(void); //Access Next Node
Person* back(void); //Access last node
};
PQueue::PQueue()
{
head = NULL;
tail = NULL;
}
bool PQueue::empty(){
return (head == NULL);
}
void PQueue::enqueue(Person *myPerson){
NodePtr np = (NodePtr) malloc(sizeof(Node));
np->data = *myPerson;
np->next = NULL;
if(empty())
{
cout << "Making into creating the first node, of the linked list" <<endl;
head = np;
tail = np;
}
else { //Queue has more the one node
Node* temp = head;
if(np->data.priority > temp->data.priority) //If the priority is greater then the rest.
{
head = temp; //Saving my head pointer
head->data = np->data; //Assigning new Data to the head pointer
head->next = temp; //Assigning the rest of the linked list back into head.
cout << "Making into creating the first node again, having to reassign." <<endl;
}
else{
//Searching where to place the node.
while(temp->data.priority > np->data.priority) //Searching if the next priority is higher then the passed.
{
cout << "Inside the while loop: " << np->data.priority << " versus "<<temp->data.priority <<endl;
if(temp->next == NULL)
break;
temp = temp->next;
}
if(temp->next == NULL && np->data.priority < temp->data.priority) //Inserting at the end.
{
cout << "Making into creating the last node" <<endl;
tail->next = np;
cout << "Passing the function of creating the last node" <<endl;
}
else //Inserting into the middle of the function.
{
cout << "Inserting in the middle of the queue" <<endl;
np->next = temp->next;
temp->next = np;
}
}
}
}
void PQueue::dequeue(){
if(empty()){
cout << "\nAttempt to remove from an empty list." << endl;
exit(1);
}
Person hold = head->data;
NodePtr temp = head;
head=head->next;
if (head == NULL) tail = NULL;
free(temp);
}
Person* PQueue::front(){
//Person &temp = head->next->data;
//Person &temp = head->data;
Person &temp = head->data;
return &temp;
}
Person* PQueue::back(){
if(empty()){
cout << "\nNo entries in list." << endl;
exit(1);
}
Person &temp = tail->data;
return &temp;
}
int main() {
cout << "Starting main" << endl;
PQueue queue1; //Creating my queue.
cout << "Created Queue" << endl;
Person tempPerson;
ifstream inFile;
inFile.open("/tmp/temp");
cout << "going into while loop" << endl;
while (inFile >> tempPerson.priority >> tempPerson.name){
cout << "The priority is " << tempPerson.priority << " the name is " << tempPerson.name <<endl;
queue1.enqueue(&tempPerson);
}
//Testing Section, trying to get .front and .back to work.
Person *testPerson;
testPerson = queue1.front();
cout << "The TEST priority is " << testPerson->priority << " the TEST name is " << testPerson->name <<endl;
/**
Person *tailPerson;
testPerson = queue1.back();
cout << "The TEST priority is " << tailPerson->priority << " the TEST name is " << tailPerson->name <<endl;
**/
queue1.dequeue();
queue1.dequeue();
queue1.dequeue();
return 0;
}
當您將新的頭條目添加到非空列表時,您錯誤地將下一個指針設置為指向右指向它所在的節點,而不是像您想要的那樣將其設置為指向鏈接列表的其余部分。
head = temp; //Saving my head pointer
head->next = temp; //Assigning the rest of the linked list back into head.
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