TopNNumbers

package com.yusufaytas.test.intercom;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.PriorityQueue;
import java.util.Queue;

public class TopNNumbers {

	private int size;
	private String path;
	Queue<Integer> queue;

	public TopNNumbers(String path, int size) {
		if (size < 0) {
			throw new IllegalArgumentException("Size must be greater than 0" + size);
		}
		this.path = path;
		this.size = size;
		this.queue = new PriorityQueue<Integer>(size);
	}

	public List<Integer> topN() {
		String line = "";
		try {
			BufferedReader reader = new BufferedReader(new FileReader(this.path));
			while ((line = reader.readLine()) != "") {
				add(Integer.parseInt(line));
			}
			reader.close();
		} catch (IOException e) {
		}
		return getNumbers();
	}

	public void add(int number) {
		if (this.queue.size() == size) {
			int min = this.queue.peek();
			if (number > min) {
				this.queue.poll();
				this.add(number);
			}
		} else {
			queue.add(number);
		}
	}

	public List<Integer> getNumbers() {
		int i = size - 1;
		List<Integer> numbers = new ArrayList<Integer>();
		int array[] = new int[size];
		while (!queue.isEmpty()) {
			array[i] = queue.poll();
			i--;
		}
		for (int j = 0; j < array.length; j++) {
			numbers.add(array[j]);
		}
		return numbers;
	}
}

M = Number of Integers
N = Capacity

This algorithm runs log(N)*M

I've used a heap to decrease complexity of add methods. I don't think we can do better than log(N) here.