队列与循环队列

复习一下队列与循环队列的实现（C语言）

1、单链队列：

typedef struct QNode{ //若不写typedef，在C中每次定义QNode需要在前面加上struct，而C++不必
    QElemType data;
    struct QNode *next;
}QNode,*QueuePtr;

typedef struct{ //若不写结构体名，则需要加上typedef
    QueuePtr front;
    QueuePtr rear;
}LinkQueue;

status InitQueue(LinkQueue &Q){  //初始化
    Q.front = Q.rear = (QueuePtr) malloc(sizeof(QNode));
    if(!Q.front)
        exit(OVERFLOW);
    Q.front -> next = NULL;
    return OK;
}

status EnQueue(LinkQueue &Q,QElemType &e){  //把元素e入队
    p = (QueuePtr) malloc(sizeof(QNode));
    if(!p)
        exit(OVERFLOW);
    p -> next = NULL;
    p -> data = e;
    Q.rear -> next = p;
    Q.rear = p;
    return OK;
}

status Dequeue(LinkQueue &Q,QElemType &e){  //删除对头元素，且把队顶元素保存在e中
    if(Q.front == Q.rear)
        return ERROR;
    p = Q.front -> next;
    e = p -> data;
    Q.front -> next = p -> next;
    if(Q.rear == p)
        Q.rear = Q.front;
    free(p);
    return OK;
}

2、循环队列

#define MAXQSIZE 100

typedef struct{
    QElemType *base;
    int front;
    int rear;
}SqQueue;

status InitQueue(SqQueue &Q){
    Q.base = (QElemType *) malloc(MAXQSIZE*sizeof(QElemType));
    if(!Q.base)
        exit(OVERFLOW);
    Q.front = Q.rear = 0;
    return OK;
}

status EnQueue(SqQueue &Q,QElemType &e){
    if((Q.rear+1)%MAXQSIZE == Q.front)  //队列已满
        return ERROR;
    Q.base[Q.rear] = e;
    Q.rear = (Q.rear+1)%MAXQSIZE;
    return OK;
}

status Dequeue(SqQueue &Q,QElemType &e){
    if(Q.front == Q.rear)
        return ERROR;
    e = Q.base[Q.front];
    Q.front = (Q.front+1)%MAXQSIZE;
    return OK;
}