/** We scramble the components of the vector. */
void scramble() {
// (See "Applied Cryptography" by Bruce Schneier)
int shuffle = size() - 1;
for (int ii = shuffle; ii > 0; ii--) {
int iiPermut = Math.abs(RandomSingleton.getInstance().nextInt()) % (ii + 1);
if (iiPermut != ii) {
Object permutObject = elementAt(ii);
setElementAt(elementAt(iiPermut), ii);
setElementAt(permutObject, iiPermut);
}
}
}
/**
* Constructs a random ranking of the numbers 1 through n. Throws an IllegalArgumentException if n
* < 1. Must run in O(n log n) time <br>
* <br>
* <strong>Note:</strong> For random number generation, use the RandomSingleton class from Project
* 1; this generator might be modified slightly for use in this project. To generate a random
* permutation of 1 through n, use the <a href=
* "http://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle#The_modern_algorithm" >"shuffle"
* algorithm</a>
*
* @param n Number of random rankings to create
* @throws IllegalArgumentException if n < 1
*/
public Ranking(int n) throws IllegalArgumentException {
// Grab our Random object (You must use this class for anything Random!)
Random rand = RandomSingleton.getInstance();
if (n < 1) { // If n is less than one, constructor will throw an
// exception.
throw new IllegalArgumentException("n has to be bigger than or equal to 1");
} else { // Otherwise it will make a shuffled permutation of n.
Ranks = new int[n];
for (int i = 0; i < n; i++) { // O(n)
Ranks[i] = i + 1;
}
for (int i = n - 1; i >= 0; i--) { // O(n)
int index = 1 + rand.nextInt(i + 1);
int temp = Ranks[index - 1];
Ranks[index - 1] = Ranks[i];
Ranks[i] = temp;
}
// Total time complexity: O(2n) = O(n)
}
}
