Learning Rust and improving with Codewars solutions

One of the frustrations with learning from some text books is that they set vague exercises at the end of a chapter without being explicit in the nature of the task and therefore no solution either….

For example “Write a function to convert text to ascii”


Replace With Alphabet Position

I’ve started to use Codewars as a tool to help brush up on the “cleverest” ways to solve a problem. The term “cleverest” being based upon peer recognition.

I’ve picked this example : https://www.codewars.com/kata/546f922b54af40e1e90001da/rust

return numeric value of a lowercase letter

My attempt…(Which does work)

fn alphabet_position(text: &str) -> String {
    let alphabet = String::from("abcdefghijklmnopqrstuvwxyz");
    let mut retvec: Vec<u8> = Vec::new();

    for c in text.to_ascii_lowercase().chars() {
        let f = alphabet.find(c);
        let res = match f {
            Some(v) => v as u8 + 1,
            _ => 0,
        if res > 0 {

    let stuff_str: String = retvec
        .join(" ");

The ‘Cleverest’ solution:

Here is the top rated solution.

So even from first glance I can see there was no need to create the “alphabet” on line 2, I could have used filter and map with closures…and used “chars” to create an iterable rather than a for loop. Much more idiomatic as well?

Why the u32 – 96 ?

Once the char is lower case, you can subtract 96 to find it’s corresponding numeric value giving a = 1, b =2, and so on.

Check out the ASCII reference

Even with my long winded solution I worked out that to remove the quotes around each of the numbers you can use

".join(" ")
fn alphabet_position(text: &str) -> String {
        .filter(|c| c >= &'a' && c <= &'z')
        .map(|c| (c as u32 - 96).to_string())
        .join(" ")

Check out the code in the Rust Playground here

After solving this I was able to learn by checking the ‘best’ solution, and I’m going to try the next one which arguably is more difficult, especially in Rust.

The next Rust challenge – “The Supermarket Queue”


The is is the link to the “shopping queue” problem. I’ll update this post in due course, as I want to solve it before checking the solution(s).

My initial idea is to identify the 3 main scenarios, and use this code for starters :

Firstly, Scenario 1 is where there is 1 queue

Secondly, Scenario 2 is where the number of tills is the same or greater than the number of customers

Finally, Scenario 3 is where there are more customers than tills

1 and 2 are “Easy” to solve.

3 is not so straightforward and this is where the double ended queue “Deque” will help, with the use of “pop_front”

The queue descends from the top, imagine it like Tetris
Another example, this time more tills

Check back soon for a working solution and a comparison against the “best” solution.

In the meantime, here’s my experimental code gist: https://gist.github.com/6d49285fa7b079ad16ea79f7305a44e5

Rust Solution = (Work-in-progress)

Python Working Solution:


If you want to know more about double ended queues and circular buffers, check the Rust Docs and this example:


Collections in Rust

If you want to know which type of collection would be suitable have a look at the Rust comparison here:


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