add shuffle method

primitiveCollections/src/main/java/org/lucares/collections/IntList.java

@@ -3,7 +3,9 @@ package org.lucares.collections;
 import java.io.Serializable;
 import java.util.Arrays;
 import java.util.List;
+import java.util.Random;
 import java.util.Spliterator.OfInt;
+import java.util.concurrent.ThreadLocalRandom;
 import java.util.stream.IntStream;
 import java.util.stream.StreamSupport;
 
@@ -483,6 +485,35 @@ public final class IntList implements Serializable, Cloneable {
 		sorted = true;
 	}
 
+	/**
+	 * Shuffles the list. The permutation is uniformly distributed.
+	 */
+	public void shuffle() {
+		shuffle(ThreadLocalRandom.current());
+	}
+
+	/**
+	 * Shuffles the list. The permutation is uniformly distributed.
+	 *
+	 * @param random
+	 *            the random number generator used
+	 */
+	public void shuffle(final Random random) {
+
+		/*
+		 * See Knuth, Donald E. Seminumerical algorithms. (1998). The Art of Computer
+		 * Programming. 2. Addison–Wesley pp. 145–146. Algorithm P and exercise 18.
+		 */
+		for (int i = size() - 1; i > 0; i--) {
+			final int other = random.nextInt(i);
+
+			final int tmp = data[other];
+			data[other] = data[i];
+			data[i] = tmp;
+		}
+		sorted = false;
+	}
+
 	private void ensureCapacity(final int newElements) {
 
 		final int requiredCapacity = size + newElements;