使用HashMap搜索功能

Question

I need to use a data structure that can provide a low search time, but don't have a need to store key, value pairs.

All I need is to check if an element exists in a collection or not.

I'm thinking of inserting all the values from an array into a hashmap (with the key and value being the same) and then perform search operations on this.

Any alternatives or is this reasonable?

Answer 1

If you don't want to maintain key-value pairs, consider using java.util.HashSet

I assume your main use case would be adding elements to it and then calling 'contains' which has O(1) complexity

Answer 2

Why do you need a HashMap for this? There are a few ArrayList Examples for this.

ArrayList , List , LinkedList

You can define the object you want to store in the List by using the diamond operator

LinkedList<String> this list now stores String values.

or as the comments suggested you can use a HashSet

HashSet<String> hashSet = new HashSet<>();
hashSet.add("Item");

Answer 3

You can go with HashSet . contains(Object o) method can help you in doing desired operation. It returns true if element is present otherwise returns false .

Answer 4

You can use Bloom Filter. it is used to test whether an element is a member of a set. False positive matches are possible, but false negatives are not – in other words, a query returns either "possibly in set" or "definitely not in set". Elements can be added to the set, but not removed (though this can be addressed with a "counting" filter); the more elements that are added to the set, the larger the probability of false positives.

Cool article on Bloom Filters.