void allsubstrings(string str,int st_index,int end_index, vector<string>& strvector)
{
    string st1,st2;
    vector<string> tempvector;
    vector<string>::iterator it;
    if(st_index == end_index)
    {
        st1.push_back(str[st_index]);
        strvector.push_back(st1);
    }
    else
    {
        allsubstrings(str,st_index+1,end_index,strvector);
        for(it = strvector.begin(); it != strvector.end(); ++it)
        {
            st2 = *it;
            st2 += str[st_index];
            tempvector.push_back(st2);
            st2.clear();
        }
        st1.push_back(str[st_index]);
        tempvector.push_back(st1);
        strvector.insert( strvector.end(), tempvector.begin(), tempvector.end() );

    }
}