Cod sursă (job #529652)

#include <fstream>
#include <cstring>
using namespace std;
ifstream in("bart.in");
ofstream out("bart.out");
char s[500001];
int pi[500001];
int main()
{
    int i,n,poz;
    in>>(s+1);
    n=strlen(s+1);
    for(i=2; i<=n; i++)
    {
        pi[i]=pi[i-1];
        while(pi[i]&&s[pi[i]+1]!=s[i])
            pi[i]=pi[pi[i]];
        if(s[pi[i]+1]==s[i])
            pi[i]++;
        if(pi[i]==0)
            poz=i;
    }
    for(i=1; i<=poz; i++)
        out<<s[i];
    return 0;
}