ðŸŽ‰ Exercism Research is now launched. Help Exercism, help science and have some fun at research.exercism.io ðŸŽ‰

Published at Nov 05 2020
·
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.

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

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

```
ï»¿using System;
public static class CollatzConjecture
{
public static int Steps(int number)
{
if (number < 1) throw new ArgumentOutOfRangeException();
if (number == 1) return 0;
if (number % 2 == 0) return 1 + Steps(number / 2);
return 1 + Steps(number * 3 + 1);
}
}
```

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?

Level up your programming skills with 3,450 exercises across 52 languages, and insightful discussion with our volunteer team of welcoming mentors.
Exercism is
**100% free forever**.

## Community comments