hw 11

import java.math.BigInteger;
import java.util.Scanner;

/**
 * Nate Wheeler
 * compsci 220
 * Hw 11
 * nrwheeler@student.stcc.edu
 *
 */
public class Combinations {

    public static BigInteger getNumberOfCombinations(int n, int k) {
        BigInteger nfact = BigInteger.ONE;
        BigInteger kfact = BigInteger.ONE;
        int h = n - k;
        BigInteger hfact = BigInteger.ONE;
        // factorial of n
        for (int i = 1; i <= n; i++)
            nfact = nfact.multiply(BigInteger.valueOf((long) i));
        // factorial of k
        for (int i = 1; i <= k; i++)
            kfact = kfact.multiply(BigInteger.valueOf((long) i));
        // factorial of the difference between n and k
        for (int i = 1; i <= h; i++)
            hfact = hfact.multiply(BigInteger.valueOf((long) i));
        // basic arithmetic
        BigInteger combin = kfact.multiply(hfact);
        combin = nfact.divide(combin);
        // number of combinations
        return combin;
    }

    public static void main(String[] args) {
        System.out.println("Enter n: ");
        Scanner ncom = new Scanner(System.in);
        System.out.println("Enter k: ");
        Scanner kcom = new Scanner(System.in);
        int n = ncom.nextInt();
        int k = kcom.nextInt();
        System.out.println("The C(n, k) is " + getNumberOfCombinations(n, k));
    }
}