Find top N elements in an Array

Question

What would be the best solution to find top N (say 10) elements in an unordered list (of say 100).

The solution which came in my head was to 1. sort it using quick s

Answer 1

You can use List and can guava's Comparators class to get the desired results. It is a highly optimized solution. Please see a sample below, which gets top 5 numbers. Api can be found here.

import java.util.Comparator;
import java.util.List;
import java.util.stream.Collector;

import org.junit.Test;

import com.google.common.collect.Comparators;
import com.google.common.collect.Lists;

public class TestComparator {

    @Test
    public void testTopN() {
        final List numbers = Lists.newArrayList(1, 3, 8, 2, 6, 4, 7, 5, 9, 0);
        final Collector> collector = Comparators.greatest(5,
                Comparator.naturalOrder());
        final List top = numbers.stream().collect(collector);
        System.out.println(top);
    }

}

Output: [9, 8, 7, 6, 5]