Queue队列

队列，和栈相反 FIFO&LILO。有两个端点，rear 和 front，插入在rear之后插入，删除在front。

可以用 array 和 linked list 实现，至于各自的优缺点，之前写的有。这里就不再赘述了

array

1. 静态的

linked list

1. 动态的

array 实现

#include<stdio.h>
#include<stdlib.h>

struct queue
{
    int front, rear, size;
    unsigned capacity;
    int * array;
};
struct queue * creatQueue(int capacity)
{
    struct queue * q = (struct queue *)malloc(sizeof(struct queue));
    q->capacity = capacity;
    q->front = 0;
    q->rear = capacity - 1;
    //这样也可以
    //q->rear = 0;
    q->size = 0;
    q->array = (int *)malloc(capacity * sizeof(int));

    return q;
}
int isEmpty(struct queue * q)
{
    return 0 == q->size ? 1 : 0;
}
int isFull(struct queue * q)
{
    return q->capacity == q->size ? 1 : 0;
}
void enQueue(struct queue * q, int data)
{
    if(isFull(q))
    {
        printf("\nThe Queue is Full");
        return ;
    }
    else
    {
        //这里刚开始不懂，数组的下标是从0开始的，写成下面那种方式也可以，不知道为什么要写成这样
        q->rear = (q->rear + 1) % (q->capacity);
        //q->array[q->rear++] = data;
        q->array[q->rear] = data;
        q->size += 1;
        printf("\n%d enqueued to Q and rear = %d", data, q->rear);
    }
}
int deQueue(struct queue * q)
{
    int num;

    if(isEmpty(q))
    {
        printf("\nThe Q is empty");
        return 0;
    }
    else
    {
        num = q->array[q->front];
        q->front = (q->front +1 ) % (q->capacity);
        q->size -= 1;
        printf("\n front = %d", q->front);
        return num;
    }
}
int getFront(struct queue * q)
{
    return q->array[q->front];
}
int getRear(struct queue * q)
{
    return q->array[q->rear];
}
int main(void)
{
    struct queue * q = creatQueue(5);

    enQueue(q, 1);
    enQueue(q, 2);
    enQueue(q, 2);
    enQueue(q, 3);
    enQueue(q, 4);
    enQueue(q, 5);

    printf("\n%d dequeue off Q", deQueue(q));
    printf("\n%d dequeue off Q", deQueue(q));
    printf("\n%d dequeue off Q", deQueue(q));
    printf("\n%d dequeue off Q", deQueue(q));
    printf("\n%d dequeue off Q", deQueue(q));
    printf("\n%d dequeue off Q", deQueue(q));
    return 0;
}

linked list实现

#include<stdio.h>
#include<stdlib.h>

struct node
{
    int data;
    struct node * next;
};
struct queue
{
    struct node * rear, * front;
};
struct node * creatNode(int data)
{
    struct node * new_node = (struct node *)malloc(sizeof(struct node));
    new_node->data = data;
    new_node->next = NULL;

    return new_node;
}
struct queue * creatQueue()
{
    struct queue * q = (struct queue * )malloc(sizeof(struct queue));
    q->rear = q->front = NULL;

    return q;
}
int isEmpty(struct queue * q)
{
    return NULL == q->front ? 1 : 0;
}
void enQueue(struct queue * q, int data)
{
    struct node * new_node = creatNode(data);

    if(NULL == q->rear && NULL == q->front)
    {
        //q->rear和q->front和new_node 指向同一块地址。可以通过其中的任意一个来修改 new_node 里的值
        q->rear = q->front = new_node;
    }
    else
    {
        //q->rear 修改了 next 值，q->front->next
        q->rear->next = new_node;
        q->rear = new_node;
    }
    printf("\n%d enqueued", data);
}
struct node * deQueue(struct queue * q)
{
    struct node * temp;
    if(NULL == q->front)
    {
        printf("\nEmpty");
        return ;
    }
    temp = q->front;
    q->front = q->front->next;
    //将元素全部删除完了
    if(NULL == q->front)
    {
        q->rear = NULL;
    }
    return temp;
}
int main(void)
{
    struct queue * q = creatQueue();
    enQueue(q, 1);
    enQueue(q, 2);
    printf("\n%d", deQueue(q)->data);
    printf("\n%d", deQueue(q)->data);
    return 0;
}