Cod sursă (job #776988)

#include <iostream>
#include <vector>
#include <bits/stdc++.h>

using namespace std;
 
ifstream fin("bart.in");
ofstream fout("bart.out");
 
int main(){
    cin.tie(0);ios::sync_with_stdio(0);
 
    string s; fin >> s;
    int p[ s.size() ];
    int n = s.size();
    p[0] = 0;
    int k = 0;
    for(int i = 1; i < n; i++){
        while(k != 0 && s[k] != s[i]){
            k = p[k - 1];
        }
 
        if(s[k] == s[i]) k++;
        p[i] = k;
    }
 
    /*cout << "p : ";
    for(int i = 0; i < n; i++) cout << p[i] << " ";
    cout << endl;*/
    
    int lp = n - p[n - 1];
    if(p[n - 1] == 0) fout << s << endl;
    else{
        fout << s.substr(0, lp) << endl;
    }
 
    return 0;
}