Sieve.rb

# The Sieve of Eratosthenes

Write a program that uses the Sieve of Eratosthenes to find all the primes from 2 up to a given number.

The Sieve of Eratosthenes is a simple, ancient algorithm for finding all prime numbers up to any given limit.

Create your range, starting at two and ending at the given limit.

The algorithm consists of repeating the following over and over:

- take the next available unmarked number in your list (it is prime)
- note: if there is no such number, you're done.
- remove all the multiples of that number (they are not prime)

When the algorithm terminates, all the numbers in the list that are not marked are prime.


class Sieve
    def self.calculate_primes(number)
        numbers = (2..number).to_a
        prime_numbers = []
        until numbers.empty?
            target = numbers.shift
            prime_numbers << target
            numbers.reject! do |number|
                number % target == 0
            end
        end
        prime_numbers
    end
end

puts Sieve.calculate_primes(10)