Show how to implement a first-in, first-out (FIFO) queue with a priority queue.
ID: 3819997 • Letter: S
Question
Show how to implement a first-in, first-out (FIFO) queue with a priority queue. Provide pseudocode for the two common queue operations: enqueue and dequeue, with error checking (i.e., how to handle the cases where the queue is empty or full.) There should be a limit on the number of elements the queue can contain and the queue should allow new elements be enqueued as long as it is not full. Also, you should use as few additional bits as possible on each element in the queue to implement the FIFO mechanism. Analyze the running time of your code and explain why.
Explanation / Answer
#include<stdio.h>
#include<stdlib.h>
struct sNode
{
int data;
struct sNode *next;
};
void push(struct sNode** top_ref, int new_data);
int pop(struct sNode** top_ref);
struct queue
{
struct sNode *stack1;
struct sNode *stack2;
};
void enQueue(struct queue *q, int x)
{
push(&q->stack1, x);
}
int deQueue(struct queue *q)
{
int x;
if(q->stack1 == NULL && q->stack2 == NULL)
{
printf("Q is empty");
getchar();
exit(0);
}
if(q->stack2 == NULL)
{
while(q->stack1 != NULL)
{
x = pop(&q->stack1);
push(&q->stack2, x);
}
}
x = pop(&q->stack2);
return x;
}
void push(struct sNode** top_ref, int new_data)
{
struct sNode* new_node =
(struct sNode*) malloc(sizeof(struct sNode));
if(new_node == NULL)
{
printf("Stack overflow ");
getchar();
exit(0);
}
new_node->data = new_data;
new_node->next = (*top_ref);
(*top_ref) = new_node;
}
int pop(struct sNode** top_ref)
{
int res;
struct sNode *top;
if(*top_ref == NULL)
{
printf("Stack overflow ");
getchar();
exit(0);
}
else
{
top = *top_ref;
res = top->data;
*top_ref = top->next;
free(top);
return res;
}
}
int main()
{
struct queue *q = (struct queue*)malloc(sizeof(struct queue));
q->stack1 = NULL;
q->stack2 = NULL;
enQueue(q, 1);
enQueue(q, 2);
enQueue(q, 3);
printf("%d ", deQueue(q));
printf("%d ", deQueue(q));
printf("%d ", deQueue(q));
getchar();
}
Output:
1 2 3