673 - Parentheses Balance, uva

#include<iostream>
#include<sstream>
#include<cstdio>
#include<stack>
#include<vector>
#include<algorithm>
#define db(a) cout << #a << " = " << a << endl;
using namespace std;
int main(){
	int t;
	scanf("%d\n", &t);
	string cadena;
	for(int i = 0; i < t; i++){
		stack pila;
		getline(cin, cadena);
		if(cadena.size() == 0) {
			printf("Yes\n");
			continue;
		}
		int len = cadena.size();
		int k = 0;
		for(; k < len; k++){
			if(cadena[k] == '(' || cadena[k] == '[')
				pila.push(cadena[k]);
			else
				if(!pila.empty() && ((pila.top() == '[' && cadena[k] == ']' )||
				(pila.top() == '(' && cadena[k] == ')'))) pila.pop();
				else break;
		}
		if(pila.empty() && k == len) printf("Yes\n");
		else printf("No\n");
	}
	return 0;
}