Collatz Conjecture (aka Project Euler Problem 14) using Benchmark library - don't copy, the point is to solve it yourself!

collatz.rb

require 'benchmark'

class Collatz
  @@collatzes = {1 => 1}

  def self.max_chain_starter_under(highest)
    (1...highest).max_by { |option| Collatz.new(option).length }
  end

  def initialize(num)
    @num = num
  end

  def length
    collatz(@num)
  end

  def collatz(num)
    @@collatzes[num] ||= 1 + (num.even? ? collatz(num/2) : collatz(num*3 + 1))
  end
  private :collatz
end

benchmark_results = Benchmark.measure do
  puts Collatz.max_chain_starter_under(1_000_000)
end

benchmark_results2 = Benchmark.measure do
  puts Collatz.max_chain_starter_under(1_000_000)
end

puts "First time running: #{benchmark_results}"
puts "Second time running: #{benchmark_results2}"