triplet.rb

class Triplet

  # Class methods
  # these generate Triplet _instances_

  def self.up_to max
    valid = []
    (1..max).each do |x|
      y = x+1
      z = y+1
      while z <= max do
        z += 1 while z**2 < x**2 + y**2
        test = Triplet.new(x, y, z)
        valid << test if test.pythagorean?
        y += 1
      end
    end
    valid
  end

  def self.where opts = {}
    matches = []
    if opts[:max_factor].present?
      matches = self.up_to(opts[:max_factor])
    end

    if opts[:min_factor].present?
      matches.reject!{ |m| m.min_factor < opts[:min_factor] }
    end

    if opts[:sum].present?
      matches.select!{ |m| m.sum == opts[:sum] }
    end

    matches
  end

  # Instance methods
  # these provide functionality to triplet _instances_

  def initialize a, b, c
    @a, @b, @c = a, b, c
    @items = [@a, @b, @c]
  end

  def min_factor
    @a
  end

  def max_factor
    @z
  end

  def sum
    @items.inject(:+)
  end

  def product
    @items.inject(:*)
  end

  def pythagorean?
    @a**2 + @b**2 == @c**2
  end

end