Compare sets inside a set

Question

I have a set like this :

Set<Set<Node>> NestedSet = new HashSet<Set<Node>>();

[[Node[0], Node[1], Node[2]], [Node[0], Node[2], Node[6]], [Node[3], Node[4], Node[5]]]

I want to compare and merge sets that are inside the nested set. [0,1,2] and [0,2,6] has element in common. so should merge them to form 0,1,2,6.

The output should be like this:

[[Node[0], Node[1], Node[2], Node[6]], [Node[3], Node[4], Node[5]]]

Is there any efficient way?

Answer 1

You can use Collections.disjoint(Collection c1, Collection c2) to check two specified collections have no elements in common.

Btw make sure your Node class implemented hashCode and equals

Set<Set<Node>> result = new HashSet<Set<Node>>();
for (Set<Node> s1 : NestedSet) {
    Optional<Set<Node>> findFirst = result.stream().filter(p -> !Collections.disjoint(s1, p)).findFirst();
    if (findFirst.isPresent()){
        findFirst.get().addAll(s1); 
    }
    else {
        result.add(s1);
    }
}