Can't traverse to vertices with unique properties in Gremlin - graph

Question

I'm looking for paths to get from one vertex to the other, avoiding vertices with properties already matched on that path.
Consider this example:
Graph graph = TinkerGraph.open();
GraphTraversalSource t = graph.traversal();
Vertex A = t.addV().property("age", 19).next();
Vertex B = t.addV().property("age", 21).next();
Vertex C = t.addV().property("age", 20).next();
Vertex D = t.addV().property("age", 21).next();
Vertex E = t.addV().property("age", 22).next();
t.V(A).addE("knows").to(B).iterate();
t.V(B).addE("knows").to(C).iterate();
t.V(C).addE("knows").to(D).iterate();
t.V(D).addE("knows").to(E).iterate();
t.V(C).addE("knows").to(E).iterate();
List<Path> paths = t.V(A)
.repeat(
out()
).times(5).emit()
.has("age", 22).path().toList();
Assert.assertEquals(1, paths.size());
I'm looking for ways to go from A to E. There are two paths:
A->B->C->D->E
A->B->C->E
What I'm looking for is just the second one, because in the first path, B and D has the same age.
I tried to filter using as and by, but I failed to scale that to whole path. For instance, I can check the vertices not to match the first vertex' property, by doing the following:
List<Path> paths = t.V(A).as("first")
.repeat(
out()
.where(P.neq("first")).by("age")
).times(5).emit()
.has("age", 22).path().toList();
Assert.assertEquals(1, paths.size());
But as you can imagine, it doesn't filter the collisions in the middle of the path. I feel like there should be an easier way to do this that I'm missing. Is there a statement like as(), but instead of replacing the previous assignment, it keeps them in an array or something? How can I achieve this?
Thanks

Answer 1

You need to compare the current age against all previously seen ages. If there's any match, let the traverser die:
t.V(A).as("a").
repeat(filter(loops().is(lt(5))).out().
not(values("age").as("current"). /* current age */
select(all, "a").unfold(). /* previous ages */
values("age").
where(eq("current"))).as("a")). /* not() negates the match */
until(has("age", 22)).
path()