Creating an tree graph from a collection of objects where only parent node is known

Question

We have a large collection of objects that we need to create a tree structure from. However, our problem is that we only know each objects parent...which makes it a bit tricky since this needs to be fast.

What is the best algorithm for creating an tree graph from a collection of objects where only parent node is known?

Answer 1

Would this be easier? You don't have to replicate the objects, do you?

List millionsOfObjects = new List&ltSomeObject>(); 
FillMillonsOfObject(); 
foreach(SomeObject someObject in millionsOfObjects) 
{ 
  someObject.GetParent().children.add(someobject)
}