sieve algorithm java code example

Example 1: sieve in java

class SieveOfEratosthenes 
{ 
    void sieveOfEratosthenes(int n) 
    { 
        // Create a boolean array "prime[0..n]" and initialize 
        // all entries it as true. A value in prime[i] will 
        // finally be false if i is Not a prime, else true. 
        boolean prime[] = new boolean[n+1]; 
        for(int i=0;i<n;i++) 
            prime[i] = true; 
          
        for(int p = 2; p*p <=n; p++) 
        { 
            // If prime[p] is not changed, then it is a prime 
            if(prime[p] == true) 
            { 
                // Update all multiples of p 
                for(int i = p*p; i <= n; i += p) 
                    prime[i] = false; 
            } 
        } 
          
        // Print all prime numbers 
        for(int i = 2; i <= n; i++) 
        { 
            if(prime[i] == true) 
                System.out.print(i + " "); 
        } 
    } 
      
    // Driver Program to test above function 
    public static void main(String args[]) 
    { 
        int n = 30; 
        System.out.print("Following are the prime numbers "); 
        System.out.println("smaller than or equal to " + n); 
        SieveOfEratosthenes g = new SieveOfEratosthenes(); 
        g.sieveOfEratosthenes(n); 
    } 
}

Example 2: prime of sieve

//sieve of eratosthenes or prime of sieve
#include<iostream>
#include<math.h>
using namespace std;
void primeofsieve(long long int n)
{
	long long int arr[n]={};
	for(int i=2;i<=sqrt(n);i++)
	{
		for(long long int j=i*i;j<=n;j+=i)
			arr[j]=1;
	}
	for(long long int i=2;i<=n;i++)
	{
	    if(arr[i]==0)
	    	cout<<i<<" ";
	}


}
int main()
{

	#ifdef _DEBUG
	freopen("input.txt", "r", stdin);
	freopen("output.txt", "w", stdout);
    #endif
	long long int n;
	cin>>n;
	cout<<"PRIME NUMBERs ARE : ";
	primeofsieve(n);
	return 0;
}