Avatar of freddie2025

freddie2025's solution

to Collatz Conjecture in the JavaScript Track

Published at Mar 28 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.

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 Javascript to install the necessary dependencies:

https://exercism.io/tracks/javascript/installation

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'));
  });
});
//
// This is only a SKELETON file for the 'Collatz Conjecture' exercise. It's been provided as a
// convenience to get you started writing code faster.
//

export const steps = (n) => {
  
  let count = 0;
  
  if (n > 0) {

    while (n != 1) {
    
      if (n % 2 === 0) {
        n = n / 2;
      }
      else {
        n = (n * 3) + 1;
      } 

      count++;
    }

    return count;
  }
  else {
    throw new Error("Only positive numbers are allowed");
  }
};

Community comments

Find this solution interesting? Ask the author a question to learn more.

What can you learn from this solution?

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?