1. 题目描述

2. 思路分析

用两个栈实现，一个栈进行入队操作，另一个栈进行出队操作。
出队操作：当出队的栈不为空时，直接进行出栈操作；如果为空，需要把入队的栈元素全部导入到出队的栈，然后再进行出栈操作

3. 代码实现

typedef int STDataType;
#define INIT_CAPACITY 4
typedef struct Stack
{
	STDataType* a;
	int top;  //栈顶
	int capacity;  //容量
}ST;

//初始化栈
void STInit(ST* ps);
//入栈
void STPush(ST* ps, STDataType x);
//出栈
void STPop(ST* ps);
//获取栈顶元素
STDataType STTop(ST* ps);
//获取栈中有效元素个数
int STSize(ST* ps);
//检测栈是否为空
bool STEmpty(ST* ps);
//销毁栈
void STDestroy(ST* ps);

void STInit(ST* ps)
{
	assert(ps);
	ps->a = NULL;
	ps->top = 0;
	ps->capacity = 0;
}

void STPush(ST* ps, STDataType x)
{
	assert(ps);
	if (ps->top == ps->capacity)
	{
		int newCapacity = ps->capacity == 0 ? INIT_CAPACITY : ps->capacity * 2;
		STDataType* tmp = (STDataType*)realloc(ps->a, sizeof(STDataType) * newCapacity);
		if (tmp == NULL)
		{
			perror("realloc failed");
			exit(-1);
		}
		ps->a = tmp;
		ps->capacity = newCapacity;
	}
	ps->a[ps->top] = x;
	ps->top++;
}

void STPop(ST* ps)
{
	assert(ps);
	//空
	assert(ps->a > 0);
	--ps->top;
}

STDataType STTop(ST* ps)
{
	assert(ps);
	//空
	assert(ps->a > 0);
	return ps->a[ps->top - 1];
}

int STSize(ST* ps)
{
	assert(ps);
	return ps->top;
}

bool STEmpty(ST* ps)
{
	assert(ps);
	return ps->top == 0;
}

void STDestroy(ST* ps)
{
	assert(ps);
	ps->a = NULL;
	ps->top = ps->capacity = 0;
}

typedef struct {
  ST pushst;
  ST popst;
} MyQueue;


MyQueue* myQueueCreate() {
  MyQueue *obj=(MyQueue*)malloc(sizeof(MyQueue));
  STInit(&obj->pushst);
  STInit(&obj->popst);
  return obj;
}

void myQueuePush(MyQueue* obj, int x) {
  STPush(&obj->pushst,x);
}

int myQueuePeek(MyQueue* obj) {
	if(STEmpty(&obj->popst))
	{
		//捯数据
    while(!STEmpty(&obj->pushst))
    {
    	STPush(&obj->popst,STTop(&obj->pushst));
      STPop(&obj->pushst);
    }
  }
  return STTop(&obj->popst);
}

int myQueuePop(MyQueue* obj) {
	int front=myQueuePeek(obj);
	STPop(&obj->popst);
	return front;
}

bool myQueueEmpty(MyQueue* obj) {
	return STEmpty(&obj->popst)&&STEmpty(&obj->pushst);
}

void myQueueFree(MyQueue* obj) {
	STDestroy(&obj->popst);
	STDestroy(&obj->pushst);
	free(obj);
}

/**
 * Your MyQueue struct will be instantiated and called as such:
 * MyQueue* obj = myQueueCreate();
 * myQueuePush(obj, x);
 
 * int param_2 = myQueuePop(obj);
 
 * int param_3 = myQueuePeek(obj);
 
 * bool param_4 = myQueueEmpty(obj);
 
 * myQueueFree(obj);
*/