craterdog.collections.primitives.RandomSorter Maven / Gradle / Ivy
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* Copyright (c) Crater Dog Technologies(TM). All Rights Reserved. *
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. *
* *
* This code is free software; you can redistribute it and/or modify it *
* under the terms of The MIT License (MIT), as published by the Open *
* Source Initiative. (See http://opensource.org/licenses/MIT) *
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package craterdog.collections.primitives;
import craterdog.collections.abstractions.*;
import craterdog.collections.interfaces.Indexed;
import craterdog.utils.RandomUtils;
import java.util.Comparator;
/**
* This sorter class implements a randomizing sort algorithm. The collection to be sorted
* is randomly reordered such that the resulting order is completely random.
*
* @author Derk Norton
* @param The type of element being sorted.
*/
public class RandomSorter extends Sorter {
@Override
public void sortCollection(SortableCollection collection, Comparator comparator) {
// see if any sorting is really required
if (collection != null && collection.getSize() > 1) {
if (collection instanceof Indexed) {
// randomize it in place
@SuppressWarnings("unchecked")
Indexed indexedCollection = (Indexed) collection;
int size = collection.getSize();
randomizeCollection(indexedCollection, size);
} else {
// convert the collection to an array
E[] array = collection.toArray();
// randomize the array
randomizeArray(array);
// convert it back to a collection
collection.removeAll();
collection.addElements(array);
}
}
}
private void randomizeCollection(Indexed indexedCollection, int size) {
for (int index = size; index > 1; index--) {
int randomIndex = RandomUtils.pickRandomIndex(index) + 1; // use ordinal based indexing
E swap = indexedCollection.getElement(index);
swap = indexedCollection.replaceElement(swap, randomIndex);
indexedCollection.replaceElement(swap, index);
}
}
private void randomizeArray(E[] array) {
int size = array.length;
for (int index = size; index > 1; index--) {
int randomIndex = RandomUtils.pickRandomIndex(index); // use zero based indexing
E swap = array[index - 1];
array[index - 1] = array[randomIndex];
array[randomIndex] = swap;
}
}
}