Handling 100! in Java / Groovy

Question

I know that BigInteger is the class to use when handling really large numbers. I wrote a simple script that calculates factorial. However, it breaks at input 25 and above.

/**
*    Calculates the factorial of a given number
*/
BigInteger fact(long n){
     def fact = 1
     while(n > 0){
         fact *= n--
     }
     return fact
}

What is the right way to handle numbers as large as 100! ?

@SotiriosDelimanolis I get answer as `0` or some negative number — An SO User, Sep 07 '14 at 18:40
Overflow. It seems like `fact` is inferred to be a `long`, not a `BigInteger`. — Sotirios Delimanolis, Sep 07 '14 at 18:42

Will · Answer 1 · 2014-09-08T14:18:54.050

Just declare fact as a BigInteger with Groovy's G suffix:

BigInteger fact(long n){
     def fact = 1G
     while(n > 0){
         fact *= n--
     }
     return fact
}  

assert fact(30) == 265252859812191058636308480000000
assert fact(25) == 15511210043330985984000000
assert fact(100) == 93326215443944152681699238856266700490715968264381621468592963895217599993229915608941463976156518286253697920827223758251185210916864000000000000000000000000

score 0 · Answer 2 · edited May 23 '17 at 12:29

0

You may try like this:

import static java.math.BigInteger.ONE

static BigInteger fact(BigInteger num) {
    num.equals(ONE) ? ONE : num.multiply(fact(num.subtract(ONE)));
}

Also check the answer given by Peter here: When calculating the factorial of 100 (100!) with Java using integers I get 0

edited May 23 '17 at 12:29

Community

1
1

answered Sep 07 '14 at 18:37

Rahul Tripathi

168,305
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Explanation, please :) – An SO User Sep 07 '14 at 18:40
1

@LittleChild:- The link which I have posted has the explanation as to why you are getting a zero pr negative number. I think its because of the overflow as the most probable guess is that the fact is taking it as long rather than BigInteger. – Rahul Tripathi Sep 07 '14 at 18:41
1

@LittleChild:- You may try to change the method defintion as `BigInteger fact(BigInteger n){` or `BigInteger fact(long n){ def fact = 1G`and check the result. – Rahul Tripathi Sep 07 '14 at 18:45

Handling 100! in Java / Groovy

2 Answers2