HashSet的 <List<Integer> &gt;时间复杂度

Question

I know HashSet has both lookup/add time complexity of O(1) . But I was worried if it has the same time complexity if the Set holds List , for me it's hard to believe it would only takes O(1), how would we do hash on a List?

Thanks

Answer 1

hashCode of List s (for example, see the implementation of AbstractList ) is a function of all the elements of the List . The same is true for the equals implementation.

Therefore lookup/add in a Set<List<SomeType>> will take O(k) where k is the size of the List you are looking for/adding. However, since k doesn't depend on the number of elements in the Set , the lookup time would still be a constant function of the number of elements of the Set , so you can still say lookup takes O(1) , since the running time of lookup/add in a Collection is calculated as a function of the number of elements in the Collection , not the size of individual elements.