hdu 4300 Clairewd’s message

#include<iostream>
#include<map>
#define maxn 100010
using namespace std;
string a,b,c;
int nextt[maxn];
map<char,char>mapp;
void change()
{
mapp.clear();
for(int i=0;i<a.size();i++)
{
mapp[a[i]]='a'+i;
}
}
void get_next()
{
nextt[0]=-1;
int l=0,k=-1;
while(l<c.size())
{
if(k==-1||c[l]==c[k]) nextt[++l]=++k;
else k=nextt[k];
}
}
int solve()
{
int j=(b.size()+1)/2,i=0;
int flag=j;
while(j<b.size())
{
if(b[j]==c[i]||i==-1) i++,j++;
else i=nextt[i];
}
//cout<<c<<"~"<<i<<endl;
return i;
}
int main()
{
cin.sync_with_stdio(false);
int t;
cin>>t;
while(t--)
{
cin>>a>>b;
change();
c="";
for(int i=0;i<b.size();i++) c+=mapp[b[i]];
get_next();
int flag=solve();
cout<<b<<c.substr(flag,b.size()-2*flag)<<endl;
}
return 0;
}