Built in test case for the binomial coefficient function. - Java java.lang

Java examples for java.lang:Math Function

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Description

Built in test case for the binomial coefficient function.

Demo Code


//package com.java2s;
import java.math.BigInteger;

public class Main {
    public static final BigInteger ZERO = new BigInteger("0", 10);
    public static final BigInteger ONE = new BigInteger("1", 10);

    /**//from   www  .j  av  a 2s.  c om
     * Built in test case for the binomial coefficient function.
     */
    private static void testBinomialCoefficient() {
        if (!binomialCoefficient(new BigInteger("64", 10),
                new BigInteger("32", 10)).equals(
                new BigInteger("1832624140942590534", 10)))
            throw new IllegalStateException();
    }

    /**
     * Computes the binomial coefficient (number of unique ways to choose k elements from a set of n elements) over BigIntegers.
     * @param n number of elements in the set
     * @param k number of elements to choose from the set
     * @return number of ways to choose k elements from n elements in the set
     */
    public static BigInteger binomialCoefficient(BigInteger n, BigInteger k) {
        BigInteger result = ONE;
        if (k.compareTo(n) > 0)
            return ZERO;
        for (BigInteger i = ONE; i.compareTo(k) < 1; i = i.add(ONE)) {
            result = result.multiply(n); //result *= n--;
            n = n.subtract(ONE);
            result = result.divide(i); //result /= i;
        }
        return result;
    }

    /**
     * Computes the binomial coefficient (number of unique ways to choose k elements from a set of n elements).
     * @param n number of elements in the set
     * @param k number of elements to choose from the set
     * @return number of ways to choose k elements from n elements in the set
     */
    public static long binomialCoefficient(long n, long k) {
        long result = 1;
        if (k > n)
            return 0;
        for (long i = 1; i <= k; i++) {
            result *= n--;
            result /= i;
        }
        return result;
    }
}

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