Gets all prime numbers below max using the sieve of sundaram method - Java java.lang

Java examples for java.lang:Math Number

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Description

Gets all prime numbers below max using the sieve of sundaram method

Demo Code


//package com.java2s;

import java.util.*;

public class Main {
    /**//from  ww  w .  j  a v  a  2s  .c  o  m
     * Gets all prime numbers below <em>max</em> using the sieve of sundaram method
     *
     * @param max Upper limit
     * @return An array of prime numbers up until <em>max</em>
     */
    public static int[] sieveOfSundaram(int max) {
        int n = max / 2;
        boolean[] isPrime = new boolean[max];

        Arrays.fill(isPrime, true);

        for (int i = 1; i < n; i++) {
            for (int j = i; j <= (n - i) / (2 * i + 1); j++) {
                isPrime[i + j + 2 * i * j] = false;
            }
        }

        int[] primes = new int[max];
        int found = 0;
        if (max > 2) {
            primes[found++] = 2;
        }
        for (int i = 1; i < n; i++) {
            if (isPrime[i]) {
                primes[found++] = i * 2 + 1;
            }
        }

        return Arrays.copyOf(primes, found);
    }
}

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