not sure if I should search or sort my hashmap

Question

Hi I have a list of people with their ages, I need to find those who are more than 30 years old, is there any possibility to search in a hashmap ? (please note that I may need

Answer 1

I'd suggest you to use NavigableMap (Implemented as TreeSet).

This implementation is a quite fast - O(log(N)), versus O(N) if you implement index based on lists.

Edit. Example:

class PersonsAgeIndex {

    private NavigableMap> ageToPersons = 
                                    new TreeMap>();

    public void addPerson( Person p ) {
        List personsWithSameAge = this.ageToPersons.get( p.age );

        if ( personsWithSameAge == null ) {
            personsWithSameAge = new LinkedList();
            this.ageToPersons.put( p.age, personsWithSameAge );
        }

        personsWithSameAge.add( p );
    }

    public List personsWithAgeLessThan( int age ) {
        List persons = new LinkedList();

        // persons with less age
        for (List tmp : this.ageToPersons.headMap( age ).values()) {
            persons.addAll( tmp );
        }

        return persons;
    }

    public List personsWithAgeInInterval( int minAge, int maxAge ) {
        List persons = new LinkedList();

        // persons with age, which: (minAge <= age <= maxAge)
        for (List tmp : this.ageToPersons.subMap( minAge, true, maxAge, true ).values()) {
            persons.addAll( tmp );
        }

        return persons;
    }

}

class Person {
    public final int age;

    public Person(int age) {
        this.age = age;
    }
}