top-down subgraphs, left-right inside subgraphs

Question

I\'d like to have my graph looks like this:

But I can only get this:

Answer 1

An update on @marapet's answer using group

digraph g {
rankdir="LR";
node[shape = circle, fontsize=14];
fontsize=18;
labeljust="l";

edge[style=invis, fontsize=12];

{ rank=same;
    0 [group=a style = invis];
    01 [style = invis];
    02 [group=b style=invis];
    0 -> 01 -> 02;
}

subgraph clusterA {
    "0A" [group=a]
    "0A" -> "1A" -> "2A";
    "2A" -> "0A" [label=".", constraint=false, style=solid];
    label="A";
}

subgraph clusterB {
    "0B" -> "1B" -> "2B";
    "2B" -> "0B" [label=".", constraint=false, style=solid];
    label="B";
}

subgraph clusterC {
    "0C" [group=b]
    "1C" [group=b]
    "0C" -> "1C" -> "2C";
    "2C" -> "0C" [label=".", constraint=false, style=solid];
    label="C";
}

0 -> "0A"[style=solid];
01 -> "0B"[style=invis];
02 -> "0C"[style=invis];

// edges between clusters
edge[constraint=false, style=solid];
"0A" -> "1B" [label=a]
"1A" -> "2B" [label=a]
"0B" -> "1C" [label=b]
"1B" -> "2C" [label=b]
}