# brunnock's solution

## to Collatz Conjecture in the JavaScript Track

Published at Aug 24 2018 · 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.

## Setup

Go through the setup instructions for ECMAScript to install the necessary dependencies:

http://exercism.io/languages/ecmascript

## Requirements

Install assignment dependencies:

``````\$ npm install
``````

## Making the test suite pass

Execute the tests with:

``````\$ npm test
``````

In the test suites all tests but the first have been skipped.

Once you get a test passing, you can enable the next one by changing `xtest` to `test`.

## 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.spec.js

``````import { steps } from './collatz-conjecture';

describe('steps()', () => {
test('zero steps for one', () => {
expect(steps(1)).toEqual(0);
});

xtest('divide if even', () => {
expect(steps(16)).toEqual(4);
});

xtest('even and odd steps', () => {
expect(steps(12)).toEqual(9);
});

xtest('Large number of even and odd steps', () => {
expect(steps(1000000)).toEqual(152);
});

xtest('zero is an error', () => {
expect(() => {
steps(0);
}).toThrow(new Error('Only positive numbers are allowed'));
});

xtest('negative value is an error', () => {
expect(() => {
steps(-15);
}).toThrow(new Error('Only positive numbers are allowed'));
});
});``````
``````function steps(n,nSteps=0) {
if (n<1) {
throw('Only positive numbers are allowed');
} else if (n===1) {
return(nSteps);
} else if (n%2===0) {
n/=2;
} else {
n = n*3 +1;
}
return steps(n, ++nSteps);
}

module.exports={steps}``````