int gemstones(vector<string> arr) {
    map<char, int> m;
    int count=0;

    for (int i=0;i<arr.size();i++)
        for (int j=0;j<arr[i].size();j++)
            if (m[arr[i][j]]==i)    m[arr[i][j]]=i+1;

    map<char, int>::iterator it=m.begin();
    while(it!=m.end())
    {
        if (it->second==arr.size())
            count++;
        it++;
    }
    return count;
}