pabloh / lazy_enum Goto Github PK

Convert to lazy any ruby enumerable.


Example 1: Return the square of the first 100 prime numbers greater than 1000

require 'mathn'
Prime.lazy.select {|x| x > 1000 }.map {|x| x**2 }.take(100)


Example 2: Find the 10001st prime. (Euler Proyect #7)

Prime.lazy.drop(10000).first


Example 3: Get the pytagorean triple which sum's equal to 1000. (Euler Proyect #9)

dove_tailing = Enumerator.new do |yielder|
  Math::Naturals.each do |z|
    0.step(z) do |y|
      0.step(z - y) do |x|
        yielder << [x, y, z - y - x]
      end
    end
  end
end

dove_tailing.lazy.select {|x,y,z| (z > y && y > x) && z**2 == x**2 + y**2 }.
  select {|x,y,z| x + y + z == 1000 }.first


Example 4: Calculate the sum of all the primes below two million. (Euler Proyect #10)

Prime.lazy.take_while {|n| n < 2_000_000 }.inject(:+)