Published at Feb 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 `dotnet test`

from within the exercise directory.

Initially, only the first test will be enabled. This is to encourage you to solve the exercise one step at a time.
Once you get the first test passing, remove the `Skip`

property from the next test and work on getting that test passing.
Once none of the tests are skipped and they are all passing, you can submit your solution
using `exercism submit CollatzConjecture.cs`

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

```
// This file was auto-generated based on version 1.2.1 of the canonical data.
using System;
using Xunit;
public class CollatzConjectureTest
{
[Fact]
public void Zero_steps_for_one()
{
Assert.Equal(0, CollatzConjecture.Steps(1));
}
[Fact(Skip = "Remove to run test")]
public void Divide_if_even()
{
Assert.Equal(4, CollatzConjecture.Steps(16));
}
[Fact(Skip = "Remove to run test")]
public void Even_and_odd_steps()
{
Assert.Equal(9, CollatzConjecture.Steps(12));
}
[Fact(Skip = "Remove to run test")]
public void Large_number_of_even_and_odd_steps()
{
Assert.Equal(152, CollatzConjecture.Steps(1000000));
}
[Fact(Skip = "Remove to run test")]
public void Zero_is_an_error()
{
Assert.Throws<ArgumentException>(() => CollatzConjecture.Steps(0));
}
[Fact(Skip = "Remove to run test")]
public void Negative_value_is_an_error()
{
Assert.Throws<ArgumentException>(() => CollatzConjecture.Steps(-15));
}
}
```

```
using System;
public static class CollatzConjecture
{
public static int Steps(int number)
{
if (number < 1)
{
throw new ArgumentException("The number must be greater than 0.");
}
if (number == 1)
{
return 0;
}
var nextStepNumber = number % 2 == 0 ? number / 2 : 3 * number + 1;
return Steps(nextStepNumber) + 1;
}
}
```

A huge amount can be learned from reading other people’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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