XeroXP · February 23, 2018 07:02 · Apr 16, 2014
diff --git a/Sample.java b/Sample.java
@@ -0,0 +1,46 @@
+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));
+	}
+}