Java 向量 HashSet 中 .add() 的时间复杂度

Question

I have two java HashSets, as below:

HashSet<Integer> H1 = new HashSet<>();
HashSet<Vector> H2 = new HashSet<>();

As the number of elements in each HashSet grows larger(and assuming some of the elements are unique, some aren't), does the time complexity of adding elements for the second HashSet(*of vectors) change(relative to the second HashSet(*of integers))? Or does the fact that the HashSet contains Vectors not effect the time complexity?

I understand the time complexity of .add() the first HashSet is(in general) O(1), but could someone clarify for H2 ?

Also, if it were instead, say, a TreeSet of Vectors, how would the time complexity of .add() change from a TreeSet of ints in that case?

Answer 1

Your question makes some false assumptions

HashSet<Integer> H1 = new HashSet<>();
HashSet<Vector> H2 = new HashSet<>();

Vector is a legacy synchronized class from Java 1.0. You're probably better off using ArrayList. Vector is also a mutable class, meaning that it may not work properly in a HashSet if the Objects it contents are changing

As the number of elements in each HashSet grows larger(and assuming some of the elements are unique, some aren't)

There cannot be non-unique elements in a Set

As the number of elements in each HashSet grows larger(and assuming some of the elements are unique, some aren't), does the time complexity of adding elements for the second HashSet(*of vectors) change(relative to the second HashSet(*of integers))? Or does the fact that the HashSet contains Vectors not effect the time complexity?

I understand the time complexity of.add() the first HashSet is(in general) O(1), but could someone clarify for H2?

Basically, larger lists will change the time complexity - not of the HashSet, but of hashcode() and equals. Also be aware that adding or removing elements from a List after it is added as a key in a hashmap / hashset will generally break the Map.

Also, if it were instead, say, a TreeSet of Vectors, how would the time complexity of.add() change from a TreeSet of ints in that case?

You can't do this, as Vector does not implement Comparable