net.jqwik.engine.properties.arbitraries.exhaustive.SetExhaustiveGenerator Maven / Gradle / Ivy

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Jqwik Engine module

There is a newer version: 1.9.1

package net.jqwik.engine.properties.arbitraries.exhaustive;

import java.util.*;

import net.jqwik.api.*;
import net.jqwik.engine.support.*;

import static net.jqwik.engine.support.MathSupport.factorial;

class SetExhaustiveGenerator implements ExhaustiveGenerator> {
	private final Arbitrary elementArbitrary;
	private final long maxCount;
	private final int minSize;
	private final int maxSize;

	static Optional calculateMaxCount(Arbitrary elementArbitrary, int minSize, int maxSize) {
		Optional> exhaustiveElement = elementArbitrary.exhaustive();
		if (!exhaustiveElement.isPresent())
			return Optional.empty();

		long elementMaxCount = exhaustiveElement.get().maxCount();
		long sum = 0;
		for (int n = minSize; n <= maxSize; n++) {
			if (n == 0) { // empty set
				sum += 1;
				continue;
			}
			if (elementMaxCount < n) { // empty set
				continue;
			}
			if (elementMaxCount > 20) {
				// MathSupport.factorial() only works till 20
				return Optional.empty();
			}
			long choices = 0;
			try {
				// TODO: Use more efficient binomial calculation, e.g. from
				// https://rosettacode.org/wiki/Evaluate_binomial_coefficients#Java
				// and move it to MathSupport
				choices = factorial(elementMaxCount) / (factorial(elementMaxCount - n) * factorial(n));
			} catch (ArithmeticException ae) {
				return Optional.empty();
			}
			if (choices > ExhaustiveGenerators.MAXIMUM_ACCEPTED_MAX_COUNT || choices < 0) { // Stop when break off point reached
				return Optional.empty();
			}
			sum += choices;
		}
		return Optional.of(sum);
	}

	SetExhaustiveGenerator(Arbitrary elementArbitrary, long maxCount, int minSize, int maxSize) {
		this.elementArbitrary = elementArbitrary;
		this.minSize = minSize;
		this.maxSize = maxSize;
		this.maxCount = maxCount;
	}

	@Override
	public Iterator> iterator() {
		return Combinatorics.setCombinations(elementArbitrary.exhaustive().get(), minSize, maxSize);
	}

	@Override
	public long maxCount() {
		return maxCount;
	}
}