Algorithms related with Randomness

Write a method to shuffle a deck of cards. It must be a perfect shuffle - in other words, each 52! permutations of the deck has to be equally likely. Assume that you are given a random number generator which is perfect. - From Cracking the Code Interview

public static void shuffleArray(int[] cards) {
   int temp, index;
   for (int i = 0; i < cards.length; i++){
     index = (int) (Math.random() * (cards.length - i)) + i;
     temp = cards[i];
     cards[i] = cards[index];
     cards[index] = temp;
   }
}

Write a method to randomly generate a set of m integers from an array of size n. Each element must have equal probability of being chosen. - From Cracking the Code Interview
public static int rand(int lower, int higher) {
 return lower + (int)(Math.random() * (higher - lower + 1));
 }
 /* pick M elements from original array. Clone original array so that
 * we don’t destroy the input. */
 public static int[] pickMRandomly(int[] original, int m) {
   int[] subset = new int[m];
   int[] array = original.clone();
   for (int j = 0; j < m; j++) {
     int index = rand(j, array.length - 1);
     subset[j] = array[index];
     array[index] = array[j]; // array[j] is now “dead”
   }
   return subset;
 }