def bfs(self, r: int):
seen = np.zeros(self.n, np.bool_)
l = []
q = ArrayQueue()
q.add(r)
seen[r] = True
while q.size() > 0:
i = q.remove()
l.append(i)
ngh = self.out_edges(i)
for k in range(0, ngh.size()):
j = ngh.get(k)
if seen[j] == False:
q.add(j)
seen[j] = True
return l
