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Published at Oct 24 2020
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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.

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

This exercise has been tested on Julia versions >=1.0.

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

```
# canonical data version: 1.2.1
using Test
include("collatz-conjecture.jl")
# canonical data
@testset "Canonical data" begin
@test collatz_steps(1) == 0
@test collatz_steps(16) == 4
@test collatz_steps(12) == 9
@test collatz_steps(1000000) == 152
@test_throws DomainError collatz_steps(0)
@test_throws DomainError collatz_steps(-15)
end
```

```
function collatz_steps(n)
n <= 0 && throw(DomainError("n must be nonnegative"))
steps = 0
while n != 1
steps += 1
n = iseven(n) ? n Ã· 2 : n = 3n + 1
end
return steps
end
```

A huge amount can be learned from reading other peopleâ€™s 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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