collatz.rb

=begin
Collatz Conjecture
Hint: recursion!
The Collatz Conjecture or 3x+1 problem can be summarized as follows:
Take any positive integer n. If n is even, divide n by 2 to get n / 2. If n is odd, multiply n by 3 and add 1 to get 3n + 1. Repeat the process indefinitely. The conjecture states that no matter which number you start with, you will always reach 1 eventually.
Given a number n, return the number of steps required to reach 1.
Example:
Starting with n = 12, the steps would be as follows:
12
6
3
10
5
16
8
4
2
1
Resulting in 9 steps. So for input n = 12, the return value would be 9.

n.even? ? n / 2 : (3*n) + 1
=end

module Collatz
  def self.steps(value)
    #  break out if we've reached 1
    return 0 if value == 1

    #  we return 1 + the result of the next value steps returns (which will be 1 or 0)
    1 + steps(value.even? ? value / 2 : value * 3 + 1)
  end
end

n = ARGV.first.to_i
throw "Positive integer please" unless n.positive?

puts Collatz.steps(n)