def dfs(self, r: int):
seen = np.zeros(self.n, np.bool_)
l = []
s = ArrayStack()
s.push(r)
while s.size() > 0:
i = s.pop()
l.append(i)
seen[i] = True
ngh = self.out_edges2(i)
for j in range(0, ngh.size()):
if seen[ngh.get(j)] == False:
s.push(ngh.get(j))
else:
continue
return l
