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POSieve of Atkin returns array... with invalid indices - Java
 

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  1. POSieve of Atkin returns array... with invalid indices - Java
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    <p>So I made a <a href="http://en.wikipedia.org/wiki/Sieve_of_Atkin" rel="nofollow">sieve of Atkin</a> algorithm to generate primes (for Project Euler problems). It returns an array of primes (int[]) called <code>primes</code>. Problem is, whenever I try accessing that array from some index (I do so in my <code>main</code> method), it throws me a <code>java.lang.ArrayIndexOutOfBounds</code> exception. Help please (and if you think my logic is away with the fairies and there is a simpler way to do this, please tell me)!</p> <pre><code>import java.lang.*; import java.util.*; public class SieveOfAtkin { public static void main(String[] stuff) { int limit = getInt("Limit?"); int[] p = getPrimes(limit); for(int i = 0; i &lt; p.length; i++) { System.out.println(p[i]); } } public static int[] getPrimes(int limit) { boolean[] isPrime = new boolean[limit + 1]; double sqrt = Math.sqrt(limit); int n = 0; for(int i = 0; i &lt; limit + 1; i++) { isPrime[i] = false; } for(int x = 0; x &lt; sqrt; x++) { for(int y = 0; y &lt; sqrt; y++) { n = 4 * x * x + y * y; if(n &lt;= limit &amp;&amp; (n % 12 == 1 || n % 12 == 5)) { isPrime[n] = !isPrime[n]; } n = 3 * x * x + y * y; if(n &lt;= limit &amp;&amp; n % 12 == 7) { isPrime[n] = !isPrime[n]; } n = 3 * x * x - y * y; if(n &lt;= limit &amp;&amp; n % 12 == 11 &amp;&amp; x &gt; y) { isPrime[n] = !isPrime[n]; } } } for(int i = 5; i &lt; sqrt; i++) { if(isPrime[i]) { for(int j = i * i; j &lt; limit; j = j + (i * i)) { isPrime[j] = false; } } } int count = 0; for(int i = 0; i &lt; isPrime.length; i++) { if(isPrime[i]) { count++; } } int[] primes = new int[count]; int found = 0; if (limit &gt; 2) { primes[found++] = 2; } if (limit &gt; 3) { primes[found++] = 3; } for (int p = 5; p &lt;= limit; p += 2) { if (isPrime[p]) { primes[found++] = p; } } return primes; } public static int getInt(String prompt) { System.out.print(prompt + " "); int integer = input.nextInt(); input.nextLine(); return integer; } } </code></pre>
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    1. USBluefire
    1. USBluefire
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    1. COYour code link doesn't go to any Java code. Please include a short but *complete* program here, within the question.
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      1. POSieve of Atkin returns array... with invalid indices - Java
      1. USJon Skeet
    2. COOops, sorry, my bad D:
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      1. USBluefire
    3. CONote that the code you've given doesn't compile, either. Why not just use the command line arguments? Change the first line to `int limit = Integer.parseInt(stuff[0]);` and get rid of your `getInt` method.
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      1. POSieve of Atkin returns array... with invalid indices - Java
      1. USJon Skeet
 

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