数据结构：栈实现

栈结构

typedef struct Stack
{
	int* a;
	int top;
	int capacity;
}S;

capacity是容量
top栈顶的位置

初始化

void Init(S* ps)//初始化可以给空，也可以给值
{
	assert(ps);
	ps->a = NULL;
	ps->capacity = 0;
	ps->top = 0;//top初始化成0和-1的意义不同
	            //初始化成0表示top标记栈顶元素的后一个位置
}

入栈

void Push(S* ps, int x)
{
	assert(ps);
	if (ps->capacity == ps->top)
	{
		int newcapacity = ps->capacity == 0 ? 4 : ps->capacity * 2;
		ps->a = (int*)realloc(ps->a, newcapacity * sizeof(int));
		if (ps->a == NULL)
			exit(-1);
		ps->capacity = newcapacity;
	}
	ps->a[ps->top] = x;
	ps->top++;
}

出栈

void Pop(S* ps)
{
	//assert(ps);
	//if (!Empty(ps))
	//{
	//	--ps->top;
	//}
	assert(ps);
	assert(ps->top > 0);
	--ps->top;
}

获取栈顶元素

int Top(S* ps)
{
	assert(ps);
	assert(ps->top > 0);
	return ps->a[ps->top - 1];
}

栈空判断

bool Empty(S* ps)
{
	assert(ps);
	return ps->top == 0;
}