swust oj 962: 括号匹配问题

#include <stdio.h>
#include <stdlib.h>
typedef char datatype;
typedef struct stack
{
	datatype* a;
	int top;
	int capacity;
}ST;

void stackinit(ST* ps)
{
	ps->a = (datatype*)malloc(sizeof(datatype) * 4);
	ps->capacity = 4;
	ps->top = 0;
}

void stackdestory(ST* ps)
{
	free(ps->a);
	ps->a = NULL;
	ps->capacity = 0;
	ps->top = 0;

}

void stackpush(ST* ps, datatype x)
{
	if (ps->capacity == ps->top)
	{
		datatype* tmp = (datatype*)realloc(ps->a, sizeof(datatype) * ps->capacity * 2);
		if (tmp == NULL) exit(-1);
		else {
			ps->a = tmp;
			ps->capacity *= 2;
		}
	}
	ps->a[ps->top] = x;
	ps->top++;
}

void stackpop(ST* ps)
{
	ps->top--;
}

datatype stacktop(ST* ps)
{
	return ps->a[ps->top - 1];
}

int stacksize(ST* ps)
{
	return ps->capacity;
}

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


bool isvaild(char* s)
{
	ST st;
	stackinit(&st);
	while (*s != '\0')
	{
		switch (*s)
		{
		case '(':
		case '[':
			stackpush(&st, *s);
			s++;
			break;
		case ')':
		case ']':
			if (stackempty(&st))
			{
				stackdestory(&st);
				return false;
			}
			char top = stacktop(&st);
			stackpop(&st);
			if ((*s == ')' && top != '(') || (*s == ']' && top != '['))
			{
				stackdestory(&st);
				return false;
			}
			else s++;
		}
	}
	bool ret = stackempty(&st);
	stackdestory(&st);
	return ret;
}

int main()
{
	char arr[1000];
	scanf("%s", arr);
	if (isvaild(arr))printf("YES");
	else printf("NO");
	return 0;
}