HDU 2328 Corporate Identity

#include <iostream>
#include <cstring>
#include <string>
#include <vector>
#include <algorithm>
using namespace std;

const int MaxSize = 210;

vector<string> a;
string suba;
int index;//find the smallest to be the pattern string

int main()
{
    while (true)
    {
        int n;
        cin >> n;
        if (n == 0)
            break;
        for (int i = 0; i < n; ++i)
        {
            string temp;
            cin >> temp;
            a.push_back(temp);
        }

        //find the smallest to be the pattern string
        int Min = MaxSize;
        for (int i = 0; i < a.size(); ++i)
        {
            if (a[i].size() < Min)
            {
                index = i;
                Min = a[i].size();
            }
        }

        string res = "";
        int Len = a[index].size();//the len of pattern string
        for (int i = 0; i < Len; ++i)//start pos
        {
            for (int j = 1; i + j <= Len; ++j)//Len of substr
            {
                suba = a[index].substr(i, j);
                int k;
                for (k = 0; k < a.size(); ++k)
                {
                    if (k == index)
                        continue;
                    if (a[k].find(suba) == -1)
                        break;
                }
                if (k == a.size())//match condition
                {
                    if (res.size() < suba.size())
                        res = suba;
                    else if (res.size() == suba.size() && res > suba)
                        res = suba;
                }
            }
        }
        if (res != "")
            cout << res << endl;
        else
            cout << "IDENTITY LOST" << endl;

        a.clear();
    }

    return 0;
}