队列--链式存储

　　带头结点的队列。

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

#define OK      1
#define ERROR   0
#define TRUE    1
#define FALSE   0

typedef int Status;
typedef int QElemType;

typedef struct QNode{
    QElemType data;
    struct QNode * next;
}QNode;

typedef QNode * QueuePtr;

typedef struct{
    int length;//记录队列长度
    QueuePtr front;//front为头指针，front->next为队首元素
    QueuePtr rear;//rear为队尾指针，指向下一次入队元素的位置
}LinkQueue;

Status visit(QElemType c){
    printf("%d ",c);
    return OK;
}

Status InitQueue(LinkQueue *Q){
    Q->front = Q->rear = (QueuePtr)malloc(sizeof(QNode));
    if( ! Q->front){
        return ERROR;
    }
    Q->front->next = NULL;
    Q->length = 0;
    return OK;
}

//销毁队列：将头结点也free掉
Status DestroyQueue(LinkQueue *Q){
    QueuePtr p;
    while(Q->front){
        p = Q->front->next;
        free(Q->front);
        Q->front = p;
    }
    Q->length = 0;
    return OK;
}

//清空队列：保留头结点
Status ClearQueue(LinkQueue *Q){
    QueuePtr p,q;
    p = Q->front->next;//p指向第一个元素
    Q->front->next = NULL;//将头节点的next指针指向空。
    while(p){
        q = p;
        p = p->next;
        free(q);
    }
    Q->length = 0;
    return OK;
}

Status QueueEmpty(LinkQueue Q){
    if(Q.front == Q.rear || Q.length==0){
        return TRUE;
    }
    return FALSE;
}

int QueueLength(LinkQueue Q){
    return Q.length;
}

Status GetHead(LinkQueue Q,QElemType *e){
    if(Q.front == Q.rear){
        return ERROR;
    }
    *e = (Q.front)->next->data;
    return OK;
}

Status EnQueue(LinkQueue *Q,QElemType e){
    QueuePtr p = (QueuePtr)malloc(sizeof(QNode));
    if( ! p){
        return ERROR;
    }
    p->data = e;
    p->next = NULL;
    Q->rear->next = p;
    Q->rear = p;//队尾指针指向新插入的元素
    Q->length++;
    return OK;
}

Status DeQueue(LinkQueue *Q,QElemType *e){
    QueuePtr p;
    if(Q->front == Q->rear){
        return ERROR;//空队
    }
    p = Q->front->next;//指向队首元素
    *e = p->data;//
    Q->front->next = p->next;
    if(p == Q->rear){
        Q->rear = Q->front;
    }
    Q->length--;
    free(p);
    return OK;
} 

Status QueueTraverse(LinkQueue Q){
    QueuePtr p = (Q.front)->next;//指向对首元素，空队时，队首元素为NULL
    while(p){
        visit(p->data);
        p = p->next;
    }
    printf("\n");
    return OK;
}

int main(){
    Status i;
    QElemType e;
    LinkQueue Q;
    int j;
    i = InitQueue(&Q);
    if(i){
        printf("成功初始化队列\n");
    } else {
        printf("初始化队列失败\n");
        return 1;
    }
    printf("队列是否为空 %d\t 队列长度是 %d\n",QueueEmpty(Q),QueueLength(Q));
    
    i = EnQueue(&Q,99);
    if(i){
        printf("成功入队99\n");
    } else {
        printf("入队99失败\n");
    }
    printf("遍历队列\t");
    QueueTraverse(Q);

    for(j = 1; j < 5; j++){
        i = EnQueue(&Q,j);
        if(i){
            printf("成功入队%d\n",j);
        } else {
            printf("入队%d失败\n",j);
        }
    }
    printf("队列是否为空 %d\t 队列长度是 %d\n",QueueEmpty(Q),QueueLength(Q));
    printf("遍历队列\t");
    QueueTraverse(Q);

    GetHead(Q,&e);
    printf("队首元素是 %d\n",e);

    for(j = 0; j < 7; j++){
        i = DeQueue(&Q,&e);
        if(i){
            printf("出队成功，出队元素是 %d\n",e);  
            printf("遍历队列\t");
            QueueTraverse(Q);
            printf("队列是否为空 %d\t 队列长度是 %d\n\n",QueueEmpty(Q),QueueLength(Q));
        } else {
            printf("出队失败\n\n");
        }
    }

    for(j = 0; j < 10; j++){
        i = EnQueue(&Q,j);
        if(i){
            printf("成功入队%d\n",j);
        } else {
            printf("入队%d失败\n",j);
        }
    }
    printf("遍历队列\t");
    QueueTraverse(Q);
    printf("队列是否为空 %d\t 队列长度是 %d\n\n",QueueEmpty(Q),QueueLength(Q));

    GetHead(Q,&e);
    printf("队首元素是 %d\n\n",e);

    printf("清空队列后\n");
    ClearQueue(&Q);
    printf("遍历队列\t");
    QueueTraverse(Q);
    printf("队列是否为空 %d\t 队列长度是 %d\n\n",QueueEmpty(Q),QueueLength(Q));

    EnQueue(&Q,99);
    DestroyQueue(&Q);
    printf("队列是否为空 %d\t 队列长度是 %d\n\n",QueueEmpty(Q),QueueLength(Q));
}