顺序队列的表示和实现

typedef struct {
    data_t    data[N];
    int    front;    /* front always points to the "cycle-head",
                     * i.e. point to the previous postion of queue front
                     */
    int    rear;    /* rear point to the rear postion element of the queue */

}sequeue_t;

sequeue_t *CreateEmptySequeue(void)
{
    sequeue_t *queue;
    queue = (sequeue_t *)malloc(sizeof(sequeue_t));
    if (NULL != queue) {
        queue->front = queue->rear = 0;
        return queue;
    } else {
        return NULL;
    }
}

int ClearSequeue(sequeue_t *queue)
{
    if (NULL != queue) {
        queue->front = queue->rear = 0;
        return 0;
    } else {
        return -1;
    }
}

int DestroySequeue(sequeue_t *queue)
{
    if (NULL != queue) {
        free(queue);
        return 0;
    } else {
        return -1;
    }
}

int EmptySequeue(sequeue_t *queue)
{
    if (NULL != queue) {
        return (queue->front == queue->rear ? 1 : 0);
    } else {
        return -1;
    }
}

int FullSequeue(sequeue_t *queue)
{
    if (NULL != queue) {
        return ((queue->rear + 1) % N == queue->front ? 1 : 0); 
    } else {
        return -1;
    }
}

int EnQueue(sequeue_t *queue, data_t x)
{
    if (NULL == queue) return -1;
    if (FullSequeue(queue)) return -1;
        
    queue->rear = (queue->rear + 1)%N;
    queue->data[queue->rear] = x;
    
    return 0;
}

int DeQueue(sequeue_t *queue, data_t *x)
{
    if (NULL == queue) return -1;
    if (EmptySequeue(queue)) return -1;
        
    if (NULL != x) {
        
        queue->front = (queue->front + 1) % N;
        *x = queue->data[queue->front];
    }
    return 0;
}

void iterate_queue(sequeue_t * queue)
{
    int i;
    
    data_t a[N];
    
    if (!queue) return;

    for (i = 0; i < N; i++) {
        a[i] = ‘_‘;
    }

    i = queue->front;
    a[i] = ‘x‘;
    
    while (i != queue->rear) {
        i++;
        i = i % N;
        a[i]= queue->data[i];
    }
    
    printf("queue = (f(%d),r(%d)) {", queue->front, queue->rear);
    
    for (i = 0; i < N; i++) {
        printf("%c ", a[i]);
    }
    printf("\b}\n");
}

int main()
{
    int i;
    data_t data;
    sequeue_t *queue;

    queue = CreateEmptySequeue();

    printf("First round!-----------------------------------------------\n");
    for (i = 0; i < 20; i++) {
        if ( !FullSequeue(queue) ) {
            printf("Enter %c: ", ‘1‘ + i);
            EnQueue(queue, ‘1‘ + i);
            iterate_queue(queue);
        } else {
            printf("queue is full\n");
            break;
        }
    }

    while ( !EmptySequeue(queue) ){
        DeQueue(queue, &data);
        printf("Out   %c: ", data);
        iterate_queue(queue);
    }

    printf("Second round!----------------------------------------------\n");
    
    for (i = 0; i < 20; i++) {
        if ( !FullSequeue(queue) ) {
            printf("Enter %c: ", ‘1‘ + i);
            EnQueue(queue, ‘1‘ + i);
            iterate_queue(queue);
        } else {
            printf("queue is full\n");
            break;
        }
    }

    while ( !EmptySequeue(queue) ){
        DeQueue(queue, &data);
        printf("Out   %c: ", data);
        iterate_queue(queue);
    }
    
    DestroySequeue(queue);

    return 0;
}

First round!-----------------------------------------------
Enter 1: queue = (f(0),r(1)) {x 1 _ _ _ _ _ _ _ _}
Enter 2: queue = (f(0),r(2)) {x 1 2 _ _ _ _ _ _ _}
Enter 3: queue = (f(0),r(3)) {x 1 2 3 _ _ _ _ _ _}
Enter 4: queue = (f(0),r(4)) {x 1 2 3 4 _ _ _ _ _}
Enter 5: queue = (f(0),r(5)) {x 1 2 3 4 5 _ _ _ _}
Enter 6: queue = (f(0),r(6)) {x 1 2 3 4 5 6 _ _ _}
Enter 7: queue = (f(0),r(7)) {x 1 2 3 4 5 6 7 _ _}
Enter 8: queue = (f(0),r(8)) {x 1 2 3 4 5 6 7 8 _}
Enter 9: queue = (f(0),r(9)) {x 1 2 3 4 5 6 7 8 9}
queue is full
Out   1: queue = (f(1),r(9)) {_ x 2 3 4 5 6 7 8 9}
Out   2: queue = (f(2),r(9)) {_ _ x 3 4 5 6 7 8 9}
Out   3: queue = (f(3),r(9)) {_ _ _ x 4 5 6 7 8 9}
Out   4: queue = (f(4),r(9)) {_ _ _ _ x 5 6 7 8 9}
Out   5: queue = (f(5),r(9)) {_ _ _ _ _ x 6 7 8 9}
Out   6: queue = (f(6),r(9)) {_ _ _ _ _ _ x 7 8 9}
Out   7: queue = (f(7),r(9)) {_ _ _ _ _ _ _ x 8 9}
Out   8: queue = (f(8),r(9)) {_ _ _ _ _ _ _ _ x 9}
Out   9: queue = (f(9),r(9)) {_ _ _ _ _ _ _ _ _ x}
Second round!----------------------------------------------
Enter 1: queue = (f(9),r(0)) {1 _ _ _ _ _ _ _ _ x}
Enter 2: queue = (f(9),r(1)) {1 2 _ _ _ _ _ _ _ x}
Enter 3: queue = (f(9),r(2)) {1 2 3 _ _ _ _ _ _ x}
Enter 4: queue = (f(9),r(3)) {1 2 3 4 _ _ _ _ _ x}
Enter 5: queue = (f(9),r(4)) {1 2 3 4 5 _ _ _ _ x}
Enter 6: queue = (f(9),r(5)) {1 2 3 4 5 6 _ _ _ x}
Enter 7: queue = (f(9),r(6)) {1 2 3 4 5 6 7 _ _ x}
Enter 8: queue = (f(9),r(7)) {1 2 3 4 5 6 7 8 _ x}
Enter 9: queue = (f(9),r(8)) {1 2 3 4 5 6 7 8 9 x}
queue is full
Out   1: queue = (f(0),r(8)) {x 2 3 4 5 6 7 8 9 _}
Out   2: queue = (f(1),r(8)) {_ x 3 4 5 6 7 8 9 _}
Out   3: queue = (f(2),r(8)) {_ _ x 4 5 6 7 8 9 _}
Out   4: queue = (f(3),r(8)) {_ _ _ x 5 6 7 8 9 _}
Out   5: queue = (f(4),r(8)) {_ _ _ _ x 6 7 8 9 _}
Out   6: queue = (f(5),r(8)) {_ _ _ _ _ x 7 8 9 _}
Out   7: queue = (f(6),r(8)) {_ _ _ _ _ _ x 8 9 _}
Out   8: queue = (f(7),r(8)) {_ _ _ _ _ _ _ x 9 _}
Out   9: queue = (f(8),r(8)) {_ _ _ _ _ _ _ _ x _}