shuffle()

/* Knuth shuffle (performance guarantee) */
private static void shuffle(int[] elements) {
    Random rand = new Random();                             // 1
    for (int i = 0; i < elements.length; i++) {             // 2
        int r = i + rand.nextInt(elements.length - i);      // 2
        swap(elements, i, r);                               // 3
    }
}