Given a number n, print all primes smaller than or equal to n. It is also given that n is a small number. For example, if n is 10, the output should be “2, 3, 5, 7”. If n is 20, the output should be “2, 3, 5, 7, 11, 13, 17, 19”.
CPP
// 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
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;
} |
Output
Following are the prime numbers smaller than or equal to 30 2 3 5 7 11 13 17 19 23 29
Time Complexity : O ( n* log(logn))
Auxiliary Space : O ( 1 )
Please refer complete article on Sieve of Eratosthenes for more details!
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