'Get the group of connected same-color stones to the given position
Keyword arguments:
position -- a tuple of (x, y)
x being the column index of the starting position of the search
y being the row index of the starting position of the search
Return:
a set of tuples consist of (x, y)s which are the same-color cluster
which contains the input single position. len(group) is size of the cluster, can be large.'

def get_group(self, position):

    (x, y) = position
    return self.group_sets[x][y]
