225. 用队列实现栈

入栈，push数据到不为空的队列。

出栈，把不为空的队列的前n-1个数据导入空队列，最后剩下的一个删掉。

队列的实现可以看这篇文章
数据结构之栈和队列

typedef int QDataType;
typedef struct QueueNode
{
	QDataType data;
	struct QueueNode* next;
}QNode;
typedef struct Queue
{
	QNode* head;
	QNode* tail;
}Queue;
void QueueInit(Queue* pq)
{
	pq->head = pq->tail = NULL;
}
void QueueDestory(Queue* pq)
{
	QNode* cur = pq->head;
	while (cur)
	{
		QNode* next = cur->next;
		free(cur);
		cur = next;
	}
	pq->head = pq->tail = NULL;
}
void QueuePush(Queue* pq, QDataType x)
{
	QNode* newnode = (QNode*)malloc(sizeof(QNode));
	newnode->data = x;
	newnode->next = NULL;
	if (pq->tail == NULL)
	{
		pq->head = pq->tail = newnode;
	}
	else
	{
		pq->tail->next = newnode;
		pq->tail = newnode;
	}
}
void QueuePop(Queue* pq)
{
	if (pq->head->next == NULL)
	{
		free(pq->head);
		pq->head = pq->tail = NULL;
	}
	else
	{
		QNode* next = pq->head->next;
		free(pq->head);
		pq->head = next;
	}
}
bool QueueEmpty(Queue* pq)
{
	return pq->head == NULL;
}
size_t QueueSize(Queue* pq)
{
	QNode* cur = pq->head;
	size_t size = 0;
	while (cur)
	{
		size++;
		cur = cur->next;
	}
	return size;
}
QDataType QueueFront(Queue* pq)
{
	return pq->head->data;
}
QDataType QueueBack(Queue* pq)
{
	return pq->tail->data;
}
typedef struct {
    Queue q1;
    Queue q2;
} MyStack;
MyStack* myStackCreate() {
    MyStack* pst=(MyStack*)malloc(sizeof(MyStack));
    QueueInit(&pst->q1);
    QueueInit(&pst->q2);
    return pst;
}
void myStackPush(MyStack* obj, int x) {
    if(!QueueEmpty(&obj->q1))
    {
        QueuePush(&obj->q1,x);
    }
    else
    {
        QueuePush(&obj->q2,x);
    }
}
int myStackPop(MyStack* obj) {
    Queue* emptyQ=&obj->q1;
    Queue* nonEmptyQ=&obj->q2;
    if(!QueueEmpty(&obj->q1))
    {
        emptyQ=&obj->q2;
        nonEmptyQ=&obj->q1;
    }
    while(QueueSize(nonEmptyQ)>1)
    {
        QueuePush(emptyQ,QueueFront(nonEmptyQ));
        QueuePop(nonEmptyQ);
    }
    int top=QueueFront(nonEmptyQ);
    QueuePop(nonEmptyQ);
    return top;
}
int myStackTop(MyStack* obj) {
    if(!QueueEmpty(&obj->q1))
    return QueueBack(&obj->q1);
    else
    return QueueBack(&obj->q2);
}
bool myStackEmpty(MyStack* obj) {
    return QueueEmpty(&obj->q1)&&QueueEmpty(&obj->q2);
}
void myStackFree(MyStack* obj) {
     QueueDestory(&obj->q1);
     QueueDestory(&obj->q2);
     free(obj);
     obj=NULL;
}