codeforces 612 C. Replace To Make Regular Bracket Sequence

  1/* ***********************************************
  2Author :111qqz
  3Created Time :2015年12月25日 星期五 22时58分50秒
  4File Name :code/cf/edu4/C.cpp
  5************************************************ */
  6
  7#include <cstdio>
  8#include <cstring>
  9#include <iostream>
 10#include <algorithm>
 11#include <vector>
 12#include <queue>
 13#include <set>
 14#include <map>
 15#include <string>
 16#include <cmath>
 17#include <cstdlib>
 18#include <ctime>
 19#define fst first
 20#define sec second
 21#define lson l,m,rt<<1
 22#define rson m+1,r,rt<<1|1
 23#define ms(a,x) memset(a,x,sizeof(a))
 24typedef long long LL;
 25#define pi pair < int ,int >
 26#define MP make_pair
 27
 28using namespace std;
 29const double eps = 1E-8;
 30const int dx4[4]={1,0,0,-1};
 31const int dy4[4]={0,-1,1,0};
 32const int inf = 0x3f3f3f3f;
 33const int N=1E6+7;
 34int len;
 35char st[N];
 36int cost = 0 ;
 37
 38char a[N];
 39int n ;
 40
 41
 42int which(char ch)
 43{
 44    if (ch=='<'||ch=='{'||ch=='('||ch=='[') return 1;
 45    return 2;
 46}
 47int kin(char ch)
 48{
 49    if (ch=='{'||ch=='}') return 1;
 50    if (ch=='['||ch==']') return 2;
 51    if (ch=='<'||ch=='>') return 3;
 52    if (ch=='('||ch==')') return 4;
 53}
 54bool ok(char x,char y)
 55{
 56    int res = 0 ;
 57    if(x=='<'||x=='{'||x=='['||x=='(') res++;
 58    if (y=='>'||y=='}'||y==']'||y==')') res++;
 59    if (res==2)
 60    {
 61	if (kin(x)!=kin(y)) cost++;
 62//	cout<<"x:"<<x<<" y:"<<y<<endl;
 63	return true;
 64    }
 65    return false;
 66}
 67
 68int main()
 69{
 70	#ifndef  ONLINE_JUDGE 
 71	freopen("code/in.txt","r",stdin);
 72  #endif
 73	cin>>st;
 74	len = strlen(st);
 75	int head = -1;
 76	int ans = 0 ;
 77
 78	for ( int i = 0 ; i < len ; i++)
 79	{
 80	    if (head==-1)
 81	    {
 82		head++;
 83		a[head] = st[i];
 84		if (which(st[i])==2)
 85		{
 86		    puts("Impossible");
 87		    return 0;
 88		}
 89
 90		continue;
 91	    }
 92		if (ok(a[head],st[i]))
 93		{
 94		    head--;
 95		}
 96		else
 97		{
 98		    head++;
 99		    a[head] = st[i];
100		}
101
102//	    cout<<"head:"<<head<<endl;
103	}
104//	cout<<"head:"<<head<<endl;
105	if (head!=-1)
106	{
107	    puts("Impossible");
108	}
109	else
110	{
111	    cout<<cost<<endl;
112	}
113
114  #ifndef ONLINE_JUDGE  
115  fclose(stdin);
116  #endif
117    return 0;
118}