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package bjc.utils.gen;
import java.util.Random;
import bjc.utils.data.IHolder;
import bjc.utils.data.IPair;
import bjc.utils.data.Identity;
import bjc.utils.funcdata.FunctionalList;
import bjc.utils.funcdata.IList;
/**
* Represents a random number generator where certain results are weighted more
* heavily than others.
*
* @author ben
*
* @param <E>
* The type of values that are randomly selected.
*/
public class WeightedRandom<E> {
/* The list of probabilities for each result */
private final IList<Integer> probabilities;
/* The list of possible results to pick from */
private final IList<E> results;
/* The source for any needed random numbers */
private final Random source;
/* The total chance for all values. */
private int totalChance;
/**
* Create a new weighted random generator with the specified source of
* randomness.
*
* @param src
* The source of randomness to use.
*/
public WeightedRandom(final Random src) {
probabilities = new FunctionalList<>();
results = new FunctionalList<>();
if (src == null) throw new NullPointerException("Source of randomness must not be null");
source = src;
}
/**
* Add a probability for a specific result to be given.
*
* @param chance
* The chance to get this result.
*
* @param result
* The result to get when the chance comes up.
*/
public void addProbability(final int chance, final E result) {
probabilities.add(chance);
results.add(result);
totalChance += chance;
}
/**
* Generate a weighted random value.
*
* @return
* A random value selected in a weighted fashion.
*/
public E generateValue() {
final IHolder<Integer> value = new Identity<>(source.nextInt(totalChance));
final IHolder<E> current = new Identity<>();
final IHolder<Boolean> picked = new Identity<>(true);
probabilities.forEachIndexed((index, probability) -> {
if (picked.unwrap(bool -> bool)) {
if (value.unwrap((number) -> number < probability)) {
current.transform((result) -> results.getByIndex(index));
picked.transform((bool) -> false);
} else {
value.transform((number) -> number - probability);
}
}
});
return current.unwrap((result) -> result);
}
/**
* Return a list of values that can be generated by this generator
*
* @return
* A list of all the values that can be generated
*/
public IList<E> getResults() {
return results;
}
/**
* Return a list containing values that can be generated paired with the
* probability of those values being generated
*
* @return
* A list of pairs of values and value probabilities
*/
public IList<IPair<Integer, E>> getValues() {
return probabilities.pairWith(results);
}
}
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