Codeforces 612C Replace To Make Regular Bracket Sequence 【stack】

C. Replace To Make Regular Bracket Sequence

time limit per test

 1 second

memory limit per test

 256 megabytes

input

 standard input

output

 standard output

You are given string s consists of opening and closing brackets of four kinds <>, {}, [], (). There are two types of brackets: opening and closing. You can replace any bracket by another of the same type. For example, you can replace < by the bracket {, but you can't replace it by ) or >.

The following definition of a regular bracket sequence is well-known, so you can be familiar with it.

Let's define a regular bracket sequence (RBS). Empty string is RBS. Let s1 and s2 be a RBS then the strings <s1>s2, {s1}s2, [s1]s2,(s1)s2 are also RBS.

For example the string "[[(){}]<>]" is RBS, but the strings "[)()" and "][()()" are not.

Determine the least number of replaces to make the string s RBS.

Input

The only line contains a non empty string s, consisting of only opening and closing brackets of four kinds. The length of s does not exceed 106.

Output

If it's impossible to get RBS from s print Impossible.

Otherwise print the least number of replaces needed to get RBS from s.

Sample test(s)

input

[<}){}

output

2

input

{()}[]

output

0

input

]]

output

Impossible

#include<stdio.h>
#include<string.h>
#include<stack>
using namespace std;
int judge(char a,char b)
{
if(a=='<'&&b=='>')
return 1;
else if(a=='('&&b==')')
return 1;
else if(a=='{'&&b=='}')
return 1;
else if(a=='['&&b==']')
return 1;
return 0;
}
char st[1000010];
int main()
{
int sum,l,i;

while(~scanf("%s",st))
{
sum=0;
stack<char>a;
l=strlen(st);
if(st[0]=='>'||st[0]=='}'||st[0]==')'||st[0]==']')
printf("Impossible\n");
else
{
a.push(st[0]);
for(i=1;i<l;i++)
{
if(st[i]=='>'||st[i]=='}'||st[i]==')'||st[i]==']')
{   if(!a.empty())
  {
if(judge(a.top(),st[i]))
a.pop();
else
{
sum++;
a.pop();
}
   }
   else
   {
    a.push(st[i]);
    break;
}
}
else
a.push(st[i]);
}
if(a.empty())
printf("%d\n",sum);
else
printf("Impossible\n");
}
}
return 0;
}