Friday, May 1, 2020

Rust playground from your own gist

The rust playground is awesome.

It allows playing with rust in the browser, without needing to install anything locally. These playgrounds / playpens are popular with newer languages. I've definitely seen with rust, go, kotlin, and others. Javascript ones allow script and css and other elements.

When editing a playground, the file can be modified, compiled, and run. The file can be exported as a direct link with the code (if it is short enough to fit in a get param). The code is also stored as a github gist under the "rust-play" user, and export links are provided to view the gist and to load a permalink to the playpen with that gist.

I haven't seen this documented anywhere, but we can use our own gist in the link!

Permalink looks like this:

version, mode and edition options configure the settings for the playground.
The gist option specified the gist to load.

Advantages to using your own gist:
  • Ownership and control
  • Notification of comments
  • Tracking of forks
  • Updates of gist are reflected in the playground
  • Edits made in the playground are lost.  The playground doesn't have update access to the gist.
  • Unexpected experience for consumers?

Try out my Playground link for gist 23727a722bff54fd20f44ef43b96466b

Embedding a single file from a github gist

Embedding a github gist

Github has improved their gists by directly providing an embed script.

This is pretty handy. From the sharing dropdown on the gist, choose embed and then copy the script tag. Paste that directly into your html (say on your super minimal blogging platform, like blogger/blogspot).

The script will embed the gist with syntax highlighting and links to view the raw gist.

Format of the script tag:
<script src="${username}/${gist_id}.js"></script>

username is optional and can be skipped:
<script src="${gist_id}.js"></script>

Embedding a single file from a gist

When our gist contains multiple files, the default embed will include all of the files. (Sorted by filename, just like in the gist). You can embed just a single file by adding the filename to a file get param.

Format of the script tag:
<script src="${username}/${gist_id}.js?file=${filename}"></script>

The username path can be skipped:

<script src="${gist_id}.js?file=${filename}"></script>

Embedded file example

Embedding from file from my gist 23727a722bff54fd20f44ef43b96466b

<script src=""></script> 

toy interiew problems in rust

2019 was my "Year of Rust".  I'd hoped to blog about that, yet here we are. :)
 Recently I've been doing random problems at random "coding-interview" sites.  This is a bit like working musical scales. Practice in flexing the low level muscle memory to allow it to fade into the background and allow thinking at a higher level.

  I mostly do them in python to work out the kinks in my algorithm (seriously, they are all about fixating on annoying edge cases.)  And then a few I work out in rust.


Today's challenge: Check If a String Is a Valid Sequence from Root to Leaves Path in a Binary Tree on

Check If a String Is a Valid Sequence from Root to Leaves Path in a Binary Tree

Given a binary tree where each path going from the root to any leaf form a valid sequence, check if a given string is a valid sequence in such binary tree.
We get the given string from the concatenation of an array of integers arr and the concatenation of all values of the nodes along a path results in a sequence in the given binary tree.


A few things to note about my solution:
  • The recursion is pretty simple and makes lovely use of the match syntax
  • rust match syntax doesn't allow matching a slice into (head, tail) as one might be used to in other pattern match languages or a lisp where all arrays are built up from recursively defined two element lists, e.g. (a, (b, (c, (d, nil))))
  • During development, I worked out all the edge case logic with the recursive calls commented out and short circuited. After getting that all working, I dug into the type issues with my intial naive attempt at executing the recursion.
  • extracting a value from a Option<RC<RefCell<T>>> requires jumping through a couple of hoops.
  • My internal recursive function has a slightly different signature than the public function. In my python solution, I was able to use the primary interface in my recursion code. Passing literal vecs as borrowed from the RefCell was just never going to work.


Now let's add some tests!
The leetcode interface handles converting tests from a text form, populating the tree and then running the algorithm. Details of their population routine are not available. Adding tests manually is ... annoying. Which makes it a good practice exercise for building RC

Rust Playpen

Full code available to edit and play with on the rust playpen