joriki’s gists

joriki / BallsInBins.java

Created March 29, 2020 14:27

Generate all configurations of balls in bins, optionally with limited capacity

	import java.util.function.Consumer;

	public class BallsInBins {
	public static void traverseConfigurations (int nballs,int nbins,Consumer<int []> consumer) {
	traverseConfigurations(nballs,nbins,Integer.MAX_VALUE,consumer);
	}

	public static void traverseConfigurations (int nballs,int nbins,int capacity,Consumer<int []> consumer) {
	recurse (new int [nbins],nballs,capacity,0,consumer);
	}

joriki / Binomials.java

Created March 29, 2020 14:25

Calculate factorials and binomial coefficients

	import java.math.BigInteger;

	public class Binomials {
	static BigInteger [] [] binomials = new BigInteger [0] [0];

	public static BigInteger binomial (int n,int k) {
	if (k < 0 \|\| n < 0)
	throw new UnsupportedOperationException ();
	if (k > n)
	return BigInteger.ZERO;

joriki / Question3600102.java

Created March 29, 2020 12:43

Count the 14-card hands drawn from a standard 52-card deck that contain at least one full house; see https://math.stackexchange.com/questions/3600102.

	import java.math.BigInteger;
	import java.util.function.Consumer;

	public class Question3600102 {
	static BigInteger count = BigInteger.ZERO;
	static BigInteger [] multiplicities = new BigInteger [5];
	static {
	for (int i = 0;i <= 4;i++)
	multiplicities [i] = Binomials.binomial(4, i);
	}

joriki / Question3597830.java

Created March 27, 2020 21:09

Count the 14-card hands drawn from a standard 52-card deck that contain at least two pairs of consecutive ranks; see https://math.stackexchange.com/questions/3597830.

	import java.math.BigInteger;
	import java.util.function.Consumer;

	public class Question3597830 {
	static BigInteger count = BigInteger.ZERO;
	static BigInteger [] multiplicities = new BigInteger [5];
	static {
	for (int i = 0;i <= 4;i++)
	multiplicities [i] = Binomials.binomial(4, i);
	}

joriki / Question3594010.java

Created March 25, 2020 09:18

Solve a digit subtraction problem; see https://math.stackexchange.com/questions/3594010.

	public class Question3594010 {
	public static void main(String [] args) {
	for (int [] p : Permutations.getPermutations (9)) {
	int n1 = getNumber(p,0);
	int n2 = getNumber(p,1);
	if (n1 - n2 == 33333)
	System.out.println(n1 + " - " + n2 + " = 33333");
	}
	}

joriki / Question3588391.java

Created March 21, 2020 14:49

Compute the number of equivalence classes of 2-colorings of the edges of the n-dimensional hypercube under rotations and reflections (see https://math.stackexchange.com/questions/3588391).

	import java.math.BigInteger;
	import java.util.HashSet;
	import java.util.Set;

	public class Question3588391 {
	public static void main(String [] args) {
	for (int n = 1;;n++) {
	int nvertices = 1 << n;
	Set<Long> edges = new HashSet<>();
	for (long direction = 0,edge = 1;direction < n;direction++,edge <<= 1)

joriki / Question3578365.java

Created March 12, 2020 10:04

Find pandigital polydivisible numbers; see https://math.stackexchange.com/questions/3578365.

	import java.math.BigInteger;

	public class Question3578365 {
	static int count;
	static BigInteger result;

	public static void main(String [] args) {
	for (int n = 2;;n += 2) {
	count = 0;
	recurse (n,BigInteger.ZERO,0,new boolean [n]);

joriki / Question3576721.java

Last active March 12, 2020 16:11

Find the empirical distribution of a ratio in a randomized Fibonacci-like recurrence and its geometric mean; see https://math.stackexchange.com/questions/3576721.

	import java.util.Random;

	public class Question3576721 {
	final static long ntrials = 10000000000L;
	final static int nbins = 1000;
	final static int nmemories = 2;
	final static int nstates = 1 << nmemories;
	final static double minlog = -1.5;
	final static double maxlog = 1.5;
	final static Random random = new Random();

joriki / Question3561819.java

Created March 10, 2020 22:32

Count the five-card hands dealt from a 52-card deck that consist of three face cards, a king and a spade (see https://math.stackexchange.com/questions/3561819).

	public class Question3561819 {
	public static void main(String [] args) {
	int count = 0;

	int [] hand = new int [5];

	for (hand [0] = 0;hand [0] < 52;hand [0]++)
	for (hand [1] = hand [0] + 1;hand [1] < 52;hand [1]++)
	for (hand [2] = hand [1] + 1;hand [2] < 52;hand [2]++)
	for (hand [3] = hand [2] + 1;hand [3] < 52;hand [3]++)

joriki / Question3570779.java

Created March 8, 2020 11:57

Count the number of different admissible score sets in Dungeons and Dragons 3.5 edition; see https://math.stackexchange.com/questions/3570779.

	public class Question3570779 {
	final static int nscores = 6;
	final static int min = 3;
	final static int max = 18;

	static int count;

	public static void main(String [] args) {
	recurse (new int [nscores],0);

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