import static java.util.Arrays.asList;

import java.util.Arrays;
import java.util.Iterator;
import java.util.List;
import java.util.Random;

import com.google.common.collect.AbstractIterator;

public class Sample {
	public static <T> Iterator<T> sOfN(final Integer sampleSize, final Integer populationSize, final Iterator<T> populationItems) {
		return new AbstractIterator<T>() {
			Integer n = sampleSize;
			Integer N = populationSize;
			Integer t = 0;
			Integer m = 0;
			Random random = new Random();
			@Override
			protected T computeNext() {
				while (m<n) {
					T next = populationItems.next();
					double u = random.nextDouble();
					if ((N-t)*u >= n-m) {
						t++;
					} else {
						t++; m++;
						return next;
					}
				}
				return endOfData();
			}
		};
	}
	
	public static void main(String[] args) {
		int[] result = new int[10];
		List<Integer> digits = asList(0,1,2,3,4,5,6,7,8,9);
		for (int i=0; i<100000; i++) {
			Iterator<Integer> sample = Sample.sOfN(3, 10, digits.iterator());
			while(sample.hasNext()) {
				result[sample.next()]++;
			}
		}
		System.out.println(Arrays.toString(result));
	}
}