// functions which checks current game board for any completed rows/columns/boxes
public void CheckBoard()
{
for (int i = 0; i <= maxNum; i++)
{
if (TheSudoku.CheckRow(i))
{
validRows.Add(i);
}
if (TheSudoku.CheckColumn(i))
{
validColumns.Add(i);
}
}
validRows.RemoveAt(0);
validColumns.RemoveAt(0);
CheckSquares();
CheckVictory();
}