How to get the factorial value

Question

I want to get the factorial value of a number. I read in a wiki that I can expect the result of 5! to be 5x4x3x2x1 = 120. Now how can I get that in Java?

BigFraction g = new BigFraction(5);
System.out.println(g.getNumerator());

This prints just 5.

In the end i want to calculate combinations in a network:

network

Which has the following formula:

example from wiki

You seem to be confusing *[fractions](http://en.wikipedia.org/wiki/Fraction_(mathematics))* and *[factorials](http://en.wikipedia.org/wiki/Factorial)*. — T.J. Crowder, Feb 19 '13 at 12:37
I assume you can start wit http://stackoverflow.com/questions/891031/is-there-a-method-that-calculates-a-factorial-in-java — Raman, Feb 19 '13 at 12:39
A naive student implementation of factorial is rarely a good idea. You ought to be looking at lngamma and binomial functions. — duffymo, Feb 19 '13 at 13:01

score 1 · Answer 1 · answered Feb 19 '13 at 12:39

1

You seem to be confusing fractions and factorials.

If you want the factorial, you can use ArithmeticUtils.factorial for that:

long factorial = ArithmeticUtils.factorial(5);
System.out.println(factorial); // "120"

answered Feb 19 '13 at 12:39

T.J. Crowder

1,031,962
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How can i deal with large numbers? `long factorial = ArithmeticUtils.factorial(89);` gives a MathArithmeticException – clankill3r Feb 19 '13 at 13:04
@clankill3r: That's a *different* question. – T.J. Crowder Feb 19 '13 at 13:04

dogbane · Answer 2 · 2013-02-19T12:47:09.313

1

Use Guava's BigIntegerMath.

To calculate the factorial i.e. n!:

BigInteger factorial = BigIntegerMath.factorial(n);

To calculate the binomial i.e. n! / (k! (n - k)!):

BigInteger binomial = BigIntegerMath.binomial(n, k);

(Similar functionality for int and long is available in IntMath and LongMath respectively.)

edited Feb 19 '13 at 12:47

answered Feb 19 '13 at 12:40

dogbane

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score 1 · Accepted Answer · answered Feb 19 '13 at 12:42

1

By the way, why not just use the plain old formula:

x=n*(n-1)/2

Where n is the number of vertices.

For this simple task, you don't have to use a computationally intensive function as a factorial...

answered Feb 19 '13 at 12:42

ppeterka

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How to get the factorial value

3 Answers3