void filling (int ar[][size])
{
    srand(time(0));
    for (int r=0; r<size; r++)
        for (int c=0; c<size; c++)
        {
        res:
            ar[r][c]=rand()%16;
            for (int e=r; r>=0; e--)
                 for (int x=c; c>=0; x--)
                      if (ar[r][c] == ar[e][x]) goto res;
        }
}