too big for BigInteger

[cool dude]

i'm trying to make a program to solve a math problem which is

Quote:

What is the largest prime factor of the number 317584931803?

the problem i'm having is that even BigInteger says its too big of a number so is there any alternatives?

[Martin]

I think there's something wrong with your algorithm, or how you're using BigInt. You could just use a long long though, the number is small enough.

[cool dude]

did u actually try it?

code:

BigInteger num = BigInteger.valueOf(317584931803);

it cleary says integer number too large. long long wats that? or is it just long?

[Martin]

A long long is a 64 bit integer. A long is just an int.

But your problem is that you're declaring BigInt wrong. You're passing it 317584931803 as an integer, which is too big for an integer. Pass it as a string instead and you'll be fine.

[cool dude]

thanks using it as a string works. another question. wat syntax do u use with BigInteger to check if it is equal to something or greater/smaller than something?

[rizzix]

If you read the docs you'll notice that BigInteger implements Comparable<BigInteger>.

Thus you can easily compare two BigIntegers.

For more info, look up Comparable.

[cool dude]

i searched on the internet but it doesn't show anything relevant.

this is the line of code i need to compareTo

code:

if (num.remainder (BigInteger.valueOf(i) == 0))

obviously i can't use the == operator because it doesn't work with BigInteger.

[[Gandalf]]

You searched the internet, yet you didn't check the Java documentation? Hey look, it's also the first thing that Google pops up: here.

[cool dude]

k thanks i figured it out. the only problem i'm getting is that i'm not getting any output.

code:

import java.math.*; public class Problem3{         public static void main(String[] args){                 BigInteger num = new BigInteger("317584931803");                 for(int i = 1; i <= 317584931803; i++){                         if (num.compareTo(num.mod (BigInteger.valueOf(i))) ==  0){                                 System.out.println(i);                         }                 }         } }

the question was:

Quote:

Problem 3

The prime factors of 13195 are 5, 7, 13 and 29.

What is the largest prime factor of the number 317584931803?

[Hikaru79]

Methinks you need to rethink your algorithm.

code:

if (num.compareTo(num.mod (BigInteger.valueOf(i))) ==  0){

This will only return true if: num == num%i. This is clearly not what you need. I think what you're looking for is:

code:

if ((num.mod (BigInteger.valueOf(i)).compareTo(BigInteger.valueOf(0)))

I'm probably missing brackets there, but that's the idea You want to check that num%i==0 .

[cool dude]

it says that it is incompatible types

[wtd]

Made better.

code:

num.mod(BigInteger.valueOf(i)).compareTo(BigInteger.ZERO)

[cool dude]

wtd wrote:

Made better.

code:

num.mod(BigInteger.valueOf(i)).compareTo(BigInteger.ZERO)

how is it better? and it still says incompatible types

[wtd]

code:

BigInteger.ZERO

Is better than:

code:

new BigInteger(0)

That's not the problem, though. Look at the loop counter.

[cool dude]

thats how i always made loop counters