sieve_of_eratosthenes.cpp File Reference

Get list of prime numbers using Sieve of Eratosthenes Sieve of Eratosthenes is an algorithm to find the primes that is between 2 to N (as defined in main). More...

#include <iostream>

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Functions
void	sieve (uint32_t N, bool *isprime)
void	print (uint32_t N, const bool *isprime)
int	main ()

Detailed Description

Get list of prime numbers using Sieve of Eratosthenes Sieve of Eratosthenes is an algorithm to find the primes that is between 2 to N (as defined in main).

Time Complexity : \(O(N \cdot\log N)\)
Space Complexity : \(O(N)\)

See also

primes_up_to_billion.cpp prime_numbers.cpp

Function Documentation

main()

int main

(

)

Main function

           {
    uint32_t N = 100;
    bool *isprime = new bool[N];
    sieve(N, isprime);
    print(N, isprime);
    delete[] isprime;
 
    return 0;
}

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print()

void print	(	uint32_t	N,
		const bool *	isprime
	)

This function prints out the primes to STDOUT

Parameters

	N	number of primes to check
[in]	isprime	a boolean array of size N identifying if i^th number is prime or not

                                            {
    for (uint32_t i = 2; i <= N; i++) {
        if (!isprime[i]) {
            std::cout << i << ' ';
        }
    }
    std::cout << std::endl;
}

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sieve()

void sieve	(	uint32_t	N,
		bool *	isprime
	)

This is the function that finds the primes and eliminates the multiples.

Parameters

	N	number of primes to check
[out]	isprime	a boolean array of size N identifying if i^th number is prime or not

                                      {
    isprime[0] = true;
    isprime[1] = true;
    for (uint32_t i = 2; i * i <= N; i++) {
        if (!isprime[i]) {
            for (uint32_t j = (i << 1); j <= N; j = j + i) {
                isprime[j] = true;
            }
        }
    }
}