问题
I was wondering how (if possible) I can go about making an adjacency list representation of a (mutable) graph via HashMap[Int, Vector[Int]]
. HashMap
would be mutable of course.
Currently I have it set as HashMap[Int, ArrayBuffer[Int]]
, but the fact that I can change each cell in the ArrayBuffer makes me uncomfortable, even though I'm fairly certain I'm not doing that. I would use a ListBuffer[Int]
but I would like fast random access to neighbors due to my need to do fast random walks on the graphs. A Vector[Int]
would solve this problem, but is there anyway to do this?
To my knowledge (tried this in the REPL), this won't work:
scala> val x = new mutable.HashMap[Int, Vector[Int]]
x: scala.collection.mutable.HashMap[Int,Vector[Int]] = Map()
scala> x(3) = Vector(1)
scala> x(3) += 4 // DOES NOT WORK
I need to be able to both append to it at any time and also access any element within it randomly (given the index). Is this possible?
Thanks! -kstruct
回答1:
Using the Vector:
x += 3 -> (x(3) :+ 4) //x.type = Map(3 -> Vector(1, 4))
You might notice that this will fail if there's no existing key, so you might like to set up your map as
val x = new mutable.HashMap[Int, Vector[Int]] withDefaultValue Vector.empty
来源:https://stackoverflow.com/questions/10358265/representing-a-graph-adjacency-list-with-hashmapint-vectorint-scala