sieve of eratosthenes c++

//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; }

int n; vector<bool> is_prime(n+1, true); is_prime[0] = is_prime[1] = false; for (int i = 2; i <= n; i++) { if (is_prime[i] && (long long)i * i <= n) { for (int j = i * i; j <= n; j += i) is_prime[j] = false; } }

// C++ program to print all primes smaller than or equal to 
// n using Sieve of Eratosthenes 
#include <bits/stdc++.h> 
using namespace std; 

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. 
	bool prime[n+1]; 
	memset(prime, true, sizeof(prime)); 

	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 greater than or 
			// equal to the square of it 
			// numbers which are multiple of p and are 
			// less than p^2 are already been marked. 
			for (int i=p*p; i<=n; i += p) 
				prime[i] = false; 
		} 
	} 

	// Print all prime numbers 
	for (int p=2; p<=n; p++) 
	if (prime[p]) 
		cout << p << " "; 
} 

// Driver Program to test above function 
int main() 
{ 
	int n = 30; 
	cout << "Following are the prime numbers smaller "
		<< " than or equal to " << n << endl; 
	SieveOfEratosthenes(n); 
	return 0; 
}

Posted by: Guest on March-13-2020

int n; vector<char> is_prime(n+1, true); is_prime[0] = is_prime[1] = false; for (int i = 2; i <= n; i++) { if (is_prime[i] && (long long)i * i <= n) { for (int j = i * i; j <= n; j += i) is_prime[j] = false; } }

#include <iostream> const int len = 30; int main() { int arr[30] = {0}; for (int i = 2; i < 30; i++) { for (int j = i * i; j < 30; j+=i) { arr[j - 1] = 1; } } for (int i = 1; i < 30; i++) { if (arr[i - 1] == 0) std::cout << i << "\t"; } }

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