ConvertCSCCSR algorithm implementation:
for each edge (u, v) in graph // calculate du degree
degree(v) += 1
offset2(v) += 1
begin = 0
for node u in graph
end = offset1(u)
for i in (begin, end)
index = indice1(i)
index2 = offset2[index]
offset2[index] += 1
indice2[index2] = u
begin = end