用栈操作实现队列的操作

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用栈实现下列队列操作：

 

• push(x)  在队列末尾添加元素x
• pop()      删除队列首的元素
• peek()   返回队列首元素但不删除它
• empty() 判断队列是否为空

struct Queue {
    int data;
    struct Queue* next;
};

typedef struct Queue Queue;

/* Create a queue */
void queueCreate(Queue *queue, int maxSize) {
    
    queue = (Queue*)malloc(sizeof(Queue));
    queue->next = NULL;
    Queue* end_of_queue = queue;
    
    while (maxSize--) {
        
        int data_in_node;
        Queue* q = (Queue*)malloc(sizeof(Queue));
        if (NULL == q)
            break;
        
        printf("Please input the data of this node: ");
        scanf("%d", &data_in_node);
        
        q->next      = end_of_queue->next;
        q->data      = data_in_node;
        end_of_queue->next  = q;
        end_of_queue = q;
    }
}

/* Push element x to the back of queue */
void queuePush(Queue *queue, int element) {
    
    Queue* q    =   (Queue*)malloc(sizeof(Queue));
    if (NULL == q)
        return ;
    Queue* end  =   queue->next;
    
    while (NULL != end->next)
        end = end->next;
        
    q->next     =   end->next;
    end->next   =   q;
}

/* Removes the element from front of queue */
void queuePop(Queue *queue) {
    if (NULL == queue->next)
        return;
        
    Queue* top  = queue->next;
    queue->next = top->next;
    free(top);
}

/* Get the front element */
int queuePeek(Queue *queue) {
    
    if (NULL == queue->next)
        return -1;
    return (queue->next->data);
}

/* Return whether the queue is empty */
bool queueEmpty(Queue *queue) {
    
    return (NULL == queue->next);
}

/* Destroy the queue */
void queueDestroy(Queue *queue) {
    
    if (NULL == queue->next)
        return ;
    
    Queue* ds     = queue->next;
    Queue* dsNext = ds->next;
    
    while (NULL != dsNext->next) {
        
        free(ds);
        ds = dsNext;
        dsNext = dsNext->next;
    }
    
    free(dsNext);
    queue->next = NULL;
}