使用链表的优先级队列

优先级队列是一种特殊类型的队列，其中每个元素都是与优先级相关联，并根据其优先级提供服务。如果元素有相同的优先级，那么根据它们在队列中的排列顺序。

元素本身的值可以用于分配优先级。例如：最高值的元素被视为最高的优先级元素。但是，在其他情况下，我们可以假设最小值的元素作为最高优先级元素。在其他情况下，我们可以根据我们的需要确定优先级。

在队列中，根据先进先出规则，而在优先级队列中，则根据优先级删除这些值。

#include <stdio.h>
#include <stdlib.h>
#define NULL ((void *)0)struct node
{int data;struct node *next;
};struct node *front, *rear;/* 初始化队列*/
void createqueue() { front = rear = NULL; }int empty()
{if (front == NULL)return 1;elsereturn 0;
}void insert(int x)
{struct node *pnode;pnode = (struct node *)malloc(sizeof(struct node));if (pnode == NULL){printf("Memory overflow. Unable to insert.\n");exit(1);}pnode->data = x;pnode->next = NULL; /*新增节点总是最后一个节点*/if (empty())front = rear = pnode;else{rear->next = pnode;rear = pnode;}
}int removes()
{int min;struct node *follow, *follow1, *p, *p1;if (empty()){printf("\nQueue Underflow. Unable to remove.");exit(1);}/* 在优先级队列中找到最小值的节点*/p = p1 = front;follow = follow1 = NULL;min = front->data;while (p != NULL){if (p->data < min){min = p->data;follow1 = follow;p1 = p;}follow = p;p = p->next;}/* 根据最小值删除节点 */if (p1 == front) /* 删除第一个节点.*/{front = front->next;if (front == NULL) /* 删除唯一的一个节点 */rear = NULL;}else if (p1 == rear) /* 删除最后一个节点 */{rear = follow1;rear->next = NULL;}else /* 删除其它节点*/follow1->next = p1->next;free(p1);return min; 
}void show()
{struct node *p;if (empty())printf("Queue empty. No data to display \n");else{printf("Queue from front to rear is as shown: \n");p = front;while (p != NULL){printf("%d ", p->data);p = p->next;}printf("\n");}
}void destroyqueue() { front = rear = NULL; }int main()
{int x, ch;createqueue();do{printf("\n******Menu******\n");printf("1:Insert \n");printf("2:Remove \n");printf("3:exit \n");printf("Enter your choice: ");scanf("%d", &ch);switch (ch){case 1:printf("Enter element to be inserted: ");scanf("%d", &x);insert(x);show();break;case 2:x = removes();printf("Element removed is: %d\n", x);show();break;case 3:break;}} while (ch != 3);destroyqueue();return 0;
}

运行结果：

插入元素

******Menu******
1:Insert
2:Remove
3:exit
Enter your choice: 1
Enter element to be inserted: 12
Queue from front to rear is as shown:
12

******Menu******
1:Insert
2:Remove
3:exit
Enter your choice: 1
Enter element to be inserted: 10
Queue from front to rear is as shown:
12 10

******Menu******
1:Insert
2:Remove
3:exit
Enter your choice: 1
Enter element to be inserted: 3
Queue from front to rear is as shown:
12 10 3

******Menu******
1:Insert
2:Remove
3:exit
Enter your choice: 1
Enter element to be inserted: 90
Queue from front to rear is as shown:
12 10 3 90

******Menu******
1:Insert
2:Remove
3:exit
Enter your choice: 1
Enter element to be inserted: 66
Queue from front to rear is as shown:
12 10 3 90 66

******Menu******
1:Insert
2:Remove
3:exit
Enter your choice: 1
Enter element to be inserted: 88
Queue from front to rear is as shown:
12 10 3 90 66 88

******Menu******
1:Insert
2:Remove
3:exit
Enter your choice: 1
Enter element to be inserted: 89
Queue from front to rear is as shown:
12 10 3 90 66 88 89

******Menu******
1:Insert
2:Remove
3:exit
Enter your choice: 1
Enter element to be inserted: 18
Queue from front to rear is as shown:
12 10 3 90 66 88 89 18

根据优先级删除，最小值具有高优先级被删除。

******Menu******
1:Insert
2:Remove
3:exit
Enter your choice: 2
Element removed is: 3
Queue from front to rear is as shown:
12 10 90 66 88 89 18

******Menu******
1:Insert
2:Remove
3:exit
Enter your choice: 2
Element removed is: 10
Queue from front to rear is as shown:
12 90 66 88 89 18

******Menu******
1:Insert
2:Remove
3:exit
Enter your choice: 2
Element removed is: 12
Queue from front to rear is as shown:
90 66 88 89 18

******Menu******
1:Insert
2:Remove
3:exit
Enter your choice: 2
Element removed is: 18
Queue from front to rear is as shown:
90 66 88 89

******Menu******
1:Insert
2:Remove
3:exit
Enter your choice: 2
Element removed is: 66
Queue from front to rear is as shown:
90 88 89

******Menu******
1:Insert
2:Remove
3:exit
Enter your choice: 2
Element removed is: 88
Queue from front to rear is as shown:
90 89

******Menu******
1:Insert
2:Remove
3:exit
Enter your choice: 2
Element removed is: 89
Queue from front to rear is as shown:
90

******Menu******
1:Insert
2:Remove
3:exit
Enter your choice: 2
Element removed is: 90
Queue empty. No data to display