Code and Life

Programming, electronics and other cool tech stuff

Project Euler Problem 2 and 3 with Clojure, Python, Javascript and C++

Continuing from my Project Euler Problem 1, here are the next two Euler problems and some reflection!

Project Euler Problem 2

The second problem asks to find the sum of even Fibonacci numbers numbers below four million. For procedural languages, this is quite walk in the park, but for me a concise method to produce the series in Clojure proved a bit of a brain nugget!

Python 3

For Python, I decided to make a simple generator that yields the Fibonacci numbers below a given treshold N. Rest is just list comprehension:

def fib(N):
    i, j = 0, 1
    while j < N:
        yield(j)
        i, j = j, i+j

print(sum(i for i in fib(4e6) if i%2==0))

C++

In C++ it's natural to just loop with a conditional addition. This time I decided to drop using namespace std; to save a few characters. Without i, j = j, i+j syntax, the temporary variable ij is a bit ugly.

#include <iostream>

int main() {
    int i=0, j=1, s=0;

    while(j<4000000) {
        if(j%2==0) s += j;
        int ij = i + j; i = j; j = ij;
    }
    std::cout << s << std::endl;
}
}

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Project Euler Problem 1 with Clojure, Python, Javascript and C++

I've long thought about learning Lisp. Some time ago I ran across Clojure and the map, set and vector implementations felt like a modern addition. It's running on top of JVM which is nice in a sense, but a major pain in the ass when installing. Well, I swallowed my wow to never install JDK again and got Clojure running quite painlessly.

To learn the ropes, I thought it would be a fun idea to rewrite Project Euler problems 1-10 with Clojure to see how it would compare against my language of choice for these types of algorithmic problems, Python.

Just to make it more fun, I decided to implement them in my second favorite language, Javascript as well. Since ECMAScript 9, it's actually a pretty powerful and concise language, and coupling it with Node.js unleashes some serious usage options outside just web pages. Npm dependency hell sucks, but that's a topic for another post. For more bare metal, I'm also doing C++ (basically sticking to C functionality until maps and sets make themselves useful). Let's see how the languages stack up!

Project Euler Problem 1

The first problem in Project Euler is simple, add up numbers below 1000 that are divisible with either 3 or 5 (or both). Modulo operator % can be used to get the remainder of a number when divided by 3 and 5, and basically we add all numbers that have either modulo as zero.

Python 3

With Python, the most concise implementation is to use the sum(iterable) and a list comprehension, netting us a nice one-liner:

print(sum(i for i in range(1000) if i%3==0 or i%5==0))

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Easy-to-Embed Svelte Components As Script Tag with Rollup

After Angular, React.js and Vue, svelte is the new and cool kid on the block. I have to admit, the compile-to-plain-javascript philosophy is nice, and what is especially cool is the fact that with Rollup.js you can easily bundle a svelte app into easy-to-embed component.

I wanted to make a simple embeddable Svelte component for a friend of mine, that would be as simple as possible to include in a blog post, web site or similar with just:

<script src="https://mydomain.com/myscript.js"></script>

The script should ideally just put the component in the same place. Turns out this is really easy with Svelte. Let's dive in!

Setting up Svelte

You may want to read more about rollup-plugin-svelte and Making an app from excellent Svelte tutorial to get more familiar with the tools used here, as I'll only cover the bare essentials.

First you need to install the necessary plugins. We'll start with Rollup and install it globally so you can just use rollup command to do things. If you want, you can also install rollup locally.

user@server:~$ sudo npm install --global rollup
user@server:~$ rollup -v
rollup v2.40.0

I initially got an error saying something about imports and after a bit of googling found out that my Ubuntu version of node was very old (node -v outputted 8.x.x when 10+ was needed) – if you encounter the same issue, upgrade to a newer node (nvm is a great too to do this).

Next make a product directory and install svelte and rollup-plugin-svelte:

user@server:~$ mkdir embed-svelte
user@server:~$ cd embed-svelte/
user@server:~/embed-svelte$ npm init

[answering to npm prompts]

user@server:~/embed-svelte$ npm install --save-dev svelte
user@server:~/embed-svelte$ npm install --save-dev rollup-plugin-svelte
user@server:~/embed-svelte$ npm install --save-dev @rollup/plugin-node-resolve

Simple Svelte component

We'll go really barebones with this tutorial, just a simple heading and a paragraph. Create a Svelte component Embed.svelte:

<script>
export let name; // from props
</script>

<h1>Hello, {name}!</h1>

<p>This component was brought to you by <a href="https://codeandlife.com/">Code
  &amp; Life</a>.</p>

Then we'll need a simple .js script to import that our mini-component and inject it to the DOM of whatever page has included the resulting script. Let's call this embed.js:

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Python on-the-fly AES encryption/decryption and transfer to AWS S3

So, I started writing a file database and toolset called fileson to take advantage of AWS S3 Glacier Deep Archive (let's just call it GDA from now on). With 1 €/mo/TB storage cost, it is essentially a dirt cheap option to store very infrequently accessed data like offsite backups.

Why not just use rclone? Well, I disliked the fact that all tools do a ton of (paid) queries against S3 when syncing. I thought a simple JSON file database should work to keep track what to copy and delete. Well, that work is progressing, but as a part of that...

Encrypting on the fly with Python and Pycrypto(dome)

I started thinking that client side encryption would be useful as well. AES is tried and tested, and it's easy to find sample code to do it. But it seems wasteful to first create encrypted files on your hard drive, then upload them to AWS and finally delete everything.

Luckily, the Python AWS SDK boto3 has a great example on how to upload a file to S3 with upload_fileobj that accepts "a readable file-like object". What does that mean? Let's find out!

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JUnzip library now supports zipping as well

I was cleaning up my code folder today and came across my JUnzip library. I realized that I added zipping to the "popular" (40 stars makes it my second most starred repo at the moment) library.

It supports "deflate" method is zlib is present, and "store" if not. You can take a look at the zipping demo code to take a deeper dive.

Additional thanks to Björn Samuelsson for his compact CRC32 routines that were used in case there's no zlib.

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Code and Life site updated to 11ty

This site has been migrated from Wordpress to 11ty based static site. I took the posts, categories, tags and comments as JSON data and made the necessary templates for conversion. Everything should be a lot faster now.

The look is still a bit bare, and some things like tables seem a bit broken. Will address these issues hopefully during upcoming days, weeks and months. Enjoy!

PS. Comments are currently disabled, I was only receiving spam in any case. You can check out my homepage at https://joonaspihlajamaa.com/ if you want to contact me.

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