ruby - collatz-conjecture

ruby/collatz-conjecture/README.md

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+# Collatz Conjecture
+
+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.
+
+## Examples
+
+Starting with n = 12, the steps would be as follows:
+
+0. 12
+1. 6
+2. 3
+3. 10
+4. 5
+5. 16
+6. 8
+7. 4
+8. 2
+9. 1
+
+Resulting in 9 steps. So for input n = 12, the return value would be 9.
+
+* * * *
+
+For installation and learning resources, refer to the
+[exercism help page](http://exercism.io/languages/ruby).
+
+For running the tests provided, you will need the Minitest gem. Open a
+terminal window and run the following command to install minitest:
+
+    gem install minitest
+
+If you would like color output, you can `require 'minitest/pride'` in
+the test file, or note the alternative instruction, below, for running
+the test file.
+
+Run the tests from the exercise directory using the following command:
+
+    ruby collatz_conjecture_test.rb
+
+To include color from the command line:
+
+    ruby -r minitest/pride collatz_conjecture_test.rb
+
+
+## Source
+
+An unsolved problem in mathematics named after mathematician Lothar Collatz [https://en.wikipedia.org/wiki/3x_%2B_1_problem](https://en.wikipedia.org/wiki/3x_%2B_1_problem)
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

ruby/collatz-conjecture/collatz_conjecture.rb

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+class CollatzConjecture
+  def self.steps(n, count = 0)
+    if n < 1
+      raise ArgumentError
+    elsif n == 1
+      count
+    else
+      count += 1
+      if n % 2 == 0
+        number = n / 2
+      else
+        number = (3 * n) + 1
+      end
+      steps(number, count)
+    end
+  end
+end

ruby/collatz-conjecture/collatz_conjecture_test.rb

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+require 'minitest/autorun'
+require_relative 'collatz_conjecture'
+
+# Common test data version: 1.2.1 d94e348
+class CollatzConjectureTest < Minitest::Test
+  def test_zero_steps_for_one
+    # skip
+    assert_equal 0, CollatzConjecture.steps(1)
+  end
+
+  def test_divide_if_even
+    # skip
+    assert_equal 4, CollatzConjecture.steps(16)
+  end
+
+  def test_even_and_odd_steps
+    # skip
+    assert_equal 9, CollatzConjecture.steps(12)
+  end
+
+  def test_large_number_of_even_and_odd_steps
+    # skip
+    assert_equal 152, CollatzConjecture.steps(1_000_000)
+  end
+
+  def test_zero_is_an_error
+    # skip
+    assert_raises(ArgumentError) do
+      CollatzConjecture.steps(0)
+    end
+  end
+
+  def test_negative_value_is_an_error
+    # skip
+    assert_raises(ArgumentError) do
+      CollatzConjecture.steps(-15)
+    end
+  end
+end