de.invation.code.toval.math.MathUtils Maven / Gradle / Ivy

Go to download
package de.invation.code.toval.math;

import java.math.BigInteger;

public class MathUtils {

	/**
	 * Calculates the factorial of number.
	 * @param number Basic number for operation
	 * @return The factorial of number
	 */
	public static BigInteger getFactorial(int number) {
		BigInteger factorial = BigInteger.ONE;
		for (int i = number; i > 1; i--) {
			factorial = factorial.multiply(new BigInteger(Integer.toString(i)));
		}
		return factorial;
	}
	
	/**
	 * Returns the binomial coefficient.

	 * For any set containing n elements, this is the number of distinct k-element subsets of it.
	 * @param n Set size
	 * @param k Subset size
	 * @return The binomial coefficient of n and k
	 */
	public static long binCoeff(int n, int k) {
		if(k>n)
			return 0;
		if(k==0 || k==n)
			return 1;
		long result = 1;
		for(int i=1; i<=k; i++) {
			result *= (n-i+1)/i;
		}
		return result;
	}
	
	/**
	 * Constucts a truth-table for the given column-number. 

	 * The number of table rows is 2^columnCount.

	 * A truth-table with three columns looks like this:

	 * (0=false, 1=true)

	 * 

	 * 
	 * 0 0 0
	 * 0 0 1
	 * 0 1 0
	 * 0 1 1
	 * 1 0 0
	 * 1 0 1
	 * 1 1 0
	 * 1 1 1
	 *   
	 *   

	 * @param colCount The number of columns.
	 * @return The constructed truth-table
	 */
	public static boolean[][] getTruthTable(int colCount){
		boolean[][] table = new boolean[colCount][(int) Math.pow(2,colCount)];
		for(int i=1; i<=colCount; i++){
			for(int j=0; j<(int) Math.pow(2, colCount); j++){
				//System.out.println(i+" "+j+" "+(int) Math.floor(j/Math.pow(2,i-1)));
				table[i-1][j] = (((int) Math.floor(j/Math.pow(2,i-1))) % 2) == 0;
			}
		}
		return table;
	}
	
	/**
	 * Returns the number of places after the decimal separator of the given number.
	 * @param  Number type
	 * @param number Basic number for operation
	 * @return The number of places after the decimal separator of number
	 */
	public static  int getRHD(N number) {
		String numberAsString = String.valueOf(number);
        return Integer.valueOf(numberAsString.substring(numberAsString.lastIndexOf('.')+1).length());
	}
	
	/**
	 * Returns the number of zeros after the decimal separator of the given number before another digit appears.
	 * @param number Basic number for operation
	 * @return The number of zeros after the decimal separator before another digit appears
	 */
	public static int getRHD(double number) {
		double n = number % 1;
		int rhd = 0;
		while((n*=10) < 1)
			rhd++;
		return ++rhd;
	}

}