How to send task to each department user once using Multi-instance

Hi Team,
I need to send a task to multiple departments,So I am using multi-instance process.I am defining department names Using TaskListiner Class as below:

public class Departments implements TaskListener{

@Override
public void notify(DelegateTask delegateTask) {
	
	List<String> departments = new ArrayList<>();
	departments.add("DEPTA");
	departments.add("DEPTB");
	departments.add("DEPTC");
	 delegateTask.addCandidateGroups(departments);
	
}

If I give the loop cardinality as 3 Then each Dept user is getting 3 times.How can I assign to 3 department users only once.
Please suggest me.
Thanks In Advance

}

Go through this blog, which will help your requirement.