Array length of a long value

[[Gandalf]]

What makes you think he was talking about C++? Maybe he was, but I'm sure you could make some even faster optimised Assembly code. Try to keep your mind open on things like this.

[rizzix]

it's simple actually... here's how you'd implement it..

#1: use a multi-dimensional rectangular array (let's take a 2D array, as a 2D array will provide for storing a maximum of (2^32 - 1)*(2^32 - 1) values... *a huge number!!*
#2: fix the ROW and COL dimension to MAX_INT
#3: create a class.. that will handle the 1D -> 2D conversion for you.


now i'm not going to create this class for you but... here's the basic mechanics behind such a class:

code:

long[][]  primes = new long[Integer.MAX_INT][Integer.MAX_INT];

basically the Nth value in the emulated 1D-array is the (row*Integer.MAX_INT+col)th value in the 2D "primes" array. so in ur long get(long n); you should basically have

code:

**refer to beard0's post**

(edit: sorry dude didn't see ur post)

note: the code is not tested... it could be wrong.. but hopefully you get the idea
also note: long may not be a large type to encompass all those values.. -,-'' You might have to use the BigDecimal class.. Or even better reduce the size of the 2D "primes" array.

[Naveg]

Well the total size of the array only needs to be a number specified by the user. As well, the array type can be boolean (ie. is the index of this value prime of not).

[rizzix]

ah well all the better then.. but you get the idea..

[beard0]

Err... did nobody read my post about 2D arrays on the previous page?

[wtd]

Hey, you know what might work? Using a two dimensional array.

[rizzix]

there's a way to do it with a 2D array?? cool!! how?

[Naveg]

would it though? In theory it would yes, but I'm still restricted by java's memory limitations...which are currently reached even before an array of MAX_INT values.

[rizzix]

ok here's my shot at a solution...

Java:

import java.util.*; import java.math.*; class test {     final static BigInteger ONE = BigInteger.ONE;     final static BigInteger ZERO = BigInteger.ZERO;         public static void main(String[] args) {         for (BigInteger i : primesTakeN(new BigInteger("10000")))             System.out.println(i);     }     public static List<BigInteger> primesTakeN(BigInteger numPrimes) {                 List<BigInteger> primes = new LinkedList<BigInteger>();         List<BigInteger> indices = new LinkedList<BigInteger>();                 for (BigInteger i = new BigInteger("2");              i.compareTo(numPrimes) < 0; i = i.add(ONE)) {             primes.add(i);             indices.add(i);         }                 Iterator<BigInteger> it = indices.iterator();         while (it.hasNext()) {             BigInteger m = it.next();             Iterator<BigInteger> it2 = it;             while(it2.hasNext()) {                 BigInteger n = it2.next();                 if (n.mod(m).equals(ZERO))                     primes.remove(n);             }         }                 return primes;     } }

Notice i've used the BigInteger class... So it should work with arbitrary long numbers... either way.. this is not the "fastest" solution (especially cuz of the BigInteger class)... but.... gah!

[HyperFlexed]

I've never seen the purpose of computing primes. I sure hope I never get the project.