我正在使用双向链表实现优先级队列等待列表。我的方法创建一个新节点（优先级和学生ID）。根据节点优先级，该方法将节点排序到队列中。
what I get is what I should get
Waitlisted: 109 in 2123 | Waitlisted: 109 in 2123
Current waitlist: 109 | Current waitlist: 109
|
Waitlisted: 105 in 2123 | Waitlisted: 105 in 2123
Current waitlist: 105 | Current waitlist: 105 109
|
Waitlisted: 108 in 2123 | Waitlisted: 108 in 2123
Current waitlist: 109 105 | Current waitlist: 105 108 109
|
Waitlisted: 106 in 2123 | Waitlisted: 106 in 2123
Current waitlist: 106 | Current waitlist: 105 106 108 109
|
Waitlisted: 107 in 2123 | Waitlisted: 107 in 2123
Current waitlist: 109 106 | Current waitlist: 105 106 107 108 109
当第一个循环中队列为空时，我能够插入一个新节点。从第二次运行开始，队列的返回值是错误的。
代码
void enqueue( PQNode** ppFront, WaitlistEntry info ){
/* create a new node to store the info */
PQNode *temp = (PQNode*)malloc(sizeof(PQNode)); //create a new node to store the info
temp->info = info;
temp->pNext = NULL;
temp->pPrev = NULL;
/* check if the LL is empty and add the new node to the front if it is */
if(*ppFront == NULL){
*ppFront = temp;
return;
}
/* check if the new node should come before the first node in the LL */
if(temp->info.iPriority > (*ppFront)->info.iPriority){
temp->pNext = *ppFront;
(*ppFront)->pPrev = temp;
*ppFront = temp;
return;
}
/* walk back through the previous nodes in the LL until the correct insertion point is found */
/* remember to also check whether the previous node is NULL */
while((*ppFront)->pNext != NULL && temp->info.iPriority <= (*ppFront)->info.iPriority){
*ppFront = (*ppFront)->pNext;
}
/* insert the new node into the place you found with your loop */
/* note you may need a special case for when the previous node is NULL */
if((*ppFront)->pNext == NULL){
(*ppFront)->pNext = temp;
temp->pPrev = *ppFront;
return;
}
temp->pPrev = *ppFront;
temp->pNext = (*ppFront)->pNext;
(*ppFront)->pNext->pPrev = temp;
(*ppFront)->pNext = temp;
return;
}
的Structs
typedef struct{
int iPriority; /* Priority of the student to be enrolled */
int iStudentID; /* ID of the student */
} WaitlistEntry;
typedef struct PQNode {
WaitlistEntry info; /* WaitlistEntry stored in the node (sorted with largest priority first) */
struct PQNode* pNext; /* Pointer to next node in the LL */
struct PQNode* pPrev; /* Pointer to previous node in the LL */
} PQNode;
typedef struct{
int iCourseNumber; /* Course number of the course */
int* iStudentIDs; /* Array of IDs of students enrolled in the course */
int iNumEnrolled; /* Number of Students currently enrolled in course */
int iMaxEnrolled; /* Max number of Students that can enroll in the course */
PQNode* pFront; /* Priority queue representing the waitlist for the course */
} Course;
我设法修改了一些代码，但我仍然卡住了。
答案 0 :(得分：1)
正如BLUEPIXY所提到的，该功能的最后一位有点不对（//编辑你在此期间改变了你的代码，我指的是你的原始代码）。当您浏览while块中的列表，然后您意识到curr是尾部时，您无法检查是否到达那里，因为temp的优先级大于尾巴或你已经到达列表的末尾，temp应该成为新的尾巴。
此外，您在错误的一侧插入temp的最后一部分。
代码的最后一部分应该是这样的
//编辑发布整个代码，我只更改了函数的最后一位，以及enqueue的参数，更容易为此编写测试代码。
void print_queue(PQNode *queue)
{
if(queue == NULL)
{
puts("empty queue");
return;
}
for(;;)
{
printf("%d (priority %d)", queue->info.iStudentID, queue->info.iPriority);
queue = queue->pNext;
if(queue == NULL)
{
puts("");
return;
}
printf(" <--> ");
}
}
void enqueue( PQNode** ppFront, int id, int prio ){
/* create a new node to store the info */
PQNode *temp = (PQNode*)malloc(sizeof(PQNode)); //create a new node to store the info
temp->info.iStudentID = id;
temp->info.iPriority = prio;
temp->pNext = NULL;
temp->pPrev = NULL;
PQNode *curr = *ppFront;
/* check if the LL is empty and add the new node to the front if it is */
if(curr == NULL){
*ppFront = temp;
return;
}
/* check if the new node should come before the first node in the LL */
if(temp->info.iPriority > curr->info.iPriority){
temp->pNext = *ppFront;
(*ppFront)->pPrev = temp;
*ppFront = temp;
return;
}
/* walk back through the previous nodes in the LL until the correct insertion point is found */
/* remember to also check whether the previous node is NULL */
while(curr->pNext != NULL && temp->info.iPriority <= curr->info.iPriority){
curr = curr->pNext;
}
/* insert the new node into the place you found with your loop */
/* note you may need a special case for when the previous node is NULL */
if(curr->pNext == NULL){
// we don't know whether the while stopped because it reached the
// final node or the priority was greater, we have to check it
if(temp->info.iPriority <= curr->info.iPriority)
{
// the priority is smaller, temp should be the tail
curr->pNext = temp;
temp->pPrev = curr;
return;
} else {
// the priority is bigger, curr should the the tail
// this case is handled by the next section
}
}
temp->pPrev = curr->pPrev;
temp->pNext = curr;
curr->pPrev->pNext = temp;
curr->pPrev = temp;
}
int main(void)
{
PQNode *queue = NULL;
enqueue(&queue, 109, 10);
enqueue(&queue, 105, 40);
enqueue(&queue, 108, 20);
enqueue(&queue, 110, 30);
enqueue(&queue, 911, 11);
enqueue(&queue, 219, 25);
print_queue(queue);
return 0;
}
我得到了
105 (priority 40) <--> 110 (priority 30) <--> 219 (priority 25) <--> 108 (priority 20) <--> 911 (priority 11) <--> 109 (priority 10)