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# David-Roark's solution

## to Collatz Conjecture in the Ruby Track

Published at Apr 30 2021 · 0 comments
Instructions
Test suite
Solution

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:

1. 12
2. 6
3. 3
4. 10
5. 5
6. 16
7. 8
8. 4
9. 2
10. 1

Resulting in 9 steps. So for input n = 12, the return value would be 9.

For installation and learning resources, refer to the Ruby resources page.

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

## Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

### collatz_conjecture_test.rb

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
class CollatzConjecture
def self.steps(n)
raise ArgumentError unless n > 0 && n.is_a?(Integer)
step = 0

while n > 1
n.even? ? n = n / 2 : n = 3*n + 1
step += 1
end

step
end
end