Users Sieve of Eratosthenes method to find all primes between 0 and n, inclusive. - Java java.lang

Java examples for java.lang:Math Prime Number

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Description

Users Sieve of Eratosthenes method to find all primes between 0 and n, inclusive.

Demo Code


//package com.java2s;
import java.util.Arrays;

public class Main {
    /**// w w w.j a va 2s .  c  o  m
     * Users Sieve of Eratosthenes method to find all primes between 0 and n, inclusive.
     * @param n
     * @return
     */
    public static boolean[] getPrimes(int n) {
        //initially, assume all values between 0 and n are primes.  
        //We'll go through this list and decide which ones are really prime
        boolean[] isPrimes = new boolean[n + 1];
        Arrays.fill(isPrimes, true);
        isPrimes[0] = false;
        isPrimes[1] = false;

        int m = (int) Math.sqrt(n);

        //find the next prime number and mark all of it's multiples as not-prime
        for (int i = 0; i <= m; i++)
            if (isPrimes[i]) {
                //remove every multiple of i since we know they won't be prime numbers 
                for (int j = i + i; j <= n; j += i)
                    isPrimes[j] = false;
            }

        return isPrimes;
    }
}

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