The Number Of Sophie Germain

main.go

package main

import "fmt"

type eratosthenesSieve struct {
	sieve []bool
	maxN  int
}

func newEratosthenesSieve(maxN int) *eratosthenesSieve {
	var sieve eratosthenesSieve

	sieve.sieve = append(sieve.sieve, false)
	sieve.sieve = append(sieve.sieve, false)
	for i := 2; i < maxN; i++ {
		sieve.sieve = append(sieve.sieve, true)
	}

	sieve.maxN = maxN

	return &sieve
}

func (s *eratosthenesSieve) fill() {
	for i := 2; i*i < s.maxN; i++ {
		if s.sieve[i] {
			for j := i * i; j < s.maxN; j += i {
				s.sieve[j] = false
			}
		}
	}
}

func (s *eratosthenesSieve) String() string {
	result := ""

	for i, isPrime := range s.sieve {
		if isPrime {
			result += fmt.Sprintf("%d ", i)
		}
	}

	return result
}

type sophieGermainNumbers struct {
	primeNumbers []bool
	filtered     []int
}

func newSofiZhemenNumbers(primeNumbers []bool) *sophieGermainNumbers {
	var model sophieGermainNumbers

	model.primeNumbers = primeNumbers

	return &model
}

func (s *sophieGermainNumbers) filterPrimeNumbers() {
	for i := 2; i < len(s.primeNumbers); i++ {
		nextPos := 2*i + 1
		if nextPos >= len(s.primeNumbers) {
			return
		}

		if s.primeNumbers[i] && s.primeNumbers[nextPos] {
			s.filtered = append(s.filtered, i)
		}
	}
}

func (s *sophieGermainNumbers) String() string {
	result := ""

	for _, n := range s.filtered {
		result += fmt.Sprintf("%d ", n)
	}

	return result
}

func main() {
	const maxNumber = 10000

	erSieve := newEratosthenesSieve(maxNumber)
	erSieve.fill()

	sofiZhemenNums := newSofiZhemenNumbers(erSieve.sieve)
	sofiZhemenNums.filterPrimeNumbers()

	fmt.Println(sofiZhemenNums)
}