栈练习2

http://wikioi.com/problem/3138/

// File Name: 3137.cpp// Author: bo_jwolf// Created Time: 2013年08月13日 星期二 15时21分34秒#include<vector>#include<list>#include<map>#include<set>#include<deque>#include<stack>#include<bitset>#include<algorithm>#include<functional>#include<numeric>#include<utility>#include<sstream>#include<iostream>#include<iomanip>#include<cstdio>#include<cmath>#include<cstdlib>#include<cstring>#include<ctime>using namespace std;int main(){int n; cin >> n; stack<int> Q ;int a , b ,flag = 1 ;for( int i = 1 ; i <= n ; ++i ){cin >> a ;if( a == 1 ){cin >> b ;Q.push( b ) ;}else{if( Q.empty() ){cout << "impossible!" << endl ;flag = 0 ;break ;}Q.pop() ;}}if( flag ) {if( Q.empty() ){cout << "impossible!" << endl ;}else{cout << Q.top() << endl ;}}return 0;}