Exercism v3 launches on Sept 1st 2021. Learn more! ๐๐๐

Published at Jan 05 2019
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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.

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.

To run the tests, run the command `busted`

from within the exercise directory.

For more detailed information about the Lua track, including how to get help if you're having trouble, please visit the exercism.io Lua language page.

An unsolved problem in mathematics named after mathematician Lothar Collatz https://en.wikipedia.org/wiki/3x_%2B_1_problem

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

```
local conjecture = require('collatz-conjecture')
describe('collatz-conjecture', function()
it('zero steps for one', function()
assert.are.equal(0, conjecture(1))
end)
it('divide if even', function()
assert.are.equal(4, conjecture(16))
end)
it('even and odd steps', function()
assert.are.equal(9, conjecture(12))
end)
it('large number of even and odd steps', function()
assert.are.equal(152, conjecture(1000000))
end)
it('zero is an error', function()
assert.has_error(
function() conjecture(0) end,
'Only positive numbers are allowed'
)
end)
it('negative value is an error', function()
assert.has_error(
function() conjecture(-15) end,
'Only positive numbers are allowed'
)
end)
end)
```

```
return function(n)
assert(n > 0, 'Only positive numbers are allowed')
function collatz(n)
if n == 1 then return 0 end
if n % 2 == 0 then return 1 + collatz(n / 2) end
return 1 + collatz(3 * n + 1)
end
return collatz(n)
end
```

A huge amount can be learned from reading other peopleโs code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

- What compromises have been made?
- Are there new concepts here that you could read more about to improve your understanding?

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