obi[2017] - codigo

#include <bits/stdc++.h>
using namespace std;
#define fr(i, a, b) for(int i = a, _= b; i < _; i++)
typedef pair<int, int> pii;
map<string, vector<pii> > mp;

int main(){
    vector<string> vs;
    int n;
    cin >> n;
    cin.ignore();
    fr(i, 0, n){
        string s;
        getline(cin, s);
        vs.push_back(s);
    }
    vs[n-1].erase(10);
    fr(i, 0, n-1)
        fr(j, i, n-1){
            string temp, t1, t2;
            t1 = vs[i], t2 = vs[j];
            temp = t1 + t2;
            fr(k, 0, 11){
                mp[temp.substr(k, 10)].push_back(make_pair(i+1, j+1));
            }

            temp.clear();
            temp = t2+t1;
            fr(k, 0, 11){
                mp[temp.substr(k, 10)].push_back(make_pair(j+1, i+1));
            }

        }

    fr(i, 1, n){
        vector<pii>::iterator j;
        for(j = mp[vs[i]].begin(); j != mp[vs[i]].end(); j++)
            if(j->first-1 < i && j->second-1 < i){
                cout << vs[i];
                return 0;
            }
    }

    cout << "ok";

    return 0;
}