# miscellaneous stuff

module Euler
  def self.eratosthenes_sieve(n)
    sieve = Array.new(n + 1, true)
    sieve[0] = false
    sieve[1] = false

    2.step(to: Math.sqrt(n)) do |i|
      if sieve[i]
        (i * i).step(to: n, by: i) do |j|
          sieve[j] = false
        end
      end
    end

    result = sieve.map_with_index { |b, i| b ? i : nil }.compact
  end

  def self.palindrome?(x)
    x.to_s.reverse == x.to_s
  end
end