数据结构与算法分析-队列

数据结构与算法分析-队列（单链表实现）

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

typedef int elementtype;

typedef struct headnode *queue;
typedef struct node     *position;
struct node {
    elementtype data;
    position    next;
};
struct headnode{
    int         size;
    position    front;
    position    rear;
};   // headnode is only use head mark, next point to follow node , rear point to the end node, size declaration the length of whole queue.

queue init_queue(void);
void delete_queue(queue Q);
int isempty(queue Q);
elementtype dequeue(queue Q);
void enqueue(elementtype data,queue Q);

queue init_queue(void)
{
    queue Q;
    Q = (queue)malloc(sizeof(struct headnode));
    Q->front = NULL;
    Q->rear  = NULL;
    Q->size  = 0;
    return Q;
}
void delete_queue(queue Q)
{
    while(!isempty(Q))
        dequeue(Q);
    free(Q);
}
int isempty(queue Q)
{
    return ((Q->front == NULL)&&(Q->rear == NULL)&&(Q->size == 0));
}
void enqueue(elementtype data,queue Q)
{
    position P;
    P = (position)malloc(sizeof(struct node));
    P->data = data;
    P->next = NULL;

    if(isempty(Q))  //when Q is empty ,the new node(P) is both front node and rear node.
        Q->front = P;
    else
        Q->rear->next = P;//when Q isn‘t empty ,the new node(P) is rear node, the front node isn‘t change, but original rear->next will point to P

    Q->rear = P;
    Q->size++;
}
elementtype dequeue(queue Q)
{
    elementtype data;
    position tem;
    if(!isempty(Q))
    {
        tem = Q->front;
        data = Q->front->data;
        Q->size--;
        Q->front = tem->next;
        if(Q->size == 0)
            Q->rear = NULL;
        free(tem);
        return data;
    }
    else
    {

        printf("enqueue : error ! Q is a empty queue !\n");
        return 0 ;
    }
}

int main(int argc ,char** argv)
{
    queue Q;
    elementtype data;
    int i = 0;
    Q = init_queue();
    printf("queue size is : %d\n\n",Q->size);
    printf("enqueue 10 datas\n");
    for(i=0;i<10;i++)
    {
        enqueue(i, Q);
    }
    printf("queue size is : %d\n\n",Q->size);
    printf("enqueue 5 datas\n");
    for(i=0;i<5;i++)
    {
        data = dequeue(Q);
        printf("dequeue data is : %d\n",data);
    }
    printf("enqueue 10 datas\n\n");
    for(i=10;i<20;i++)
    {
        enqueue(i, Q);
    }
    printf("queue size is : %d\n",Q->size);

    for(i=0;i<15;i++)
    {
        data = dequeue(Q);
        printf("dequeue data is : %d\n",data);
    }
    printf("queue size is : %d\n",Q->size);
}