there's my IO template for rust: 53175781. Yeah, it's not pretty, but it is very, very fast, on par with fastest C++ templates (getchar etc).

Also rust compiler version on codeforces is a bit outdated, so you need to put

[package]
edition = "2015"

into your Cargo.toml

Regarding

Very few mutable variables.

C++ has const, but it's not the default, and it's inconvenient to use them because of std::cin.

Very strict type-checking.

g++ also have -Wconversion for warning for e.g. conversion from long long to int. I often use it and it's quite useful (although it's annoying that it doesn't recognize that (long long)a*b%MOD can be converted to int safely if MOD is an int.

I tried using Rust one year ago. Here's my template: https://codeforces.me/contest/1036/submission/42644334. It's written for Rust 1.15 (atCoder still hasn't updated since) that's why it contains some weird workarounds. It supports reading in tuples, which makes the input very nice in my opinion, especially together with automatic type inference:

fn main() {
    init(); // would not be needed anymore today by using something similar to lazy_static
    let n: usize = read(); // explicitly writing the type
    let mut lines = Vec::new();
    for _ in 0..n {
        let (a, b, c, d) = read(); // type is automatically inferred
        lines.push((Point { x: a, y: b }, Point { x: c, y: d }));
    }
    ...
}

I had to do my own I/O implementation anyways, since stdin() and stdout() are impossible to use efficiently (every time you read or write something, a mutex gets locked and I tested that that's already too slow for some tasks).

Note that I have written my own debug!() macro before dbg!() even existed (or was discussed about).

My two main reason against Rust are the lack of a good codebook (there's this one which is pretty good though: https://github.com/hatoo/competitive-rust-snippets -- it even comes with its snippet library: https://github.com/hatoo/cargo-snippet) and that I am turned down by the old compilers available on CF and atCoder. Now that CF has updated, I might give it another try.

The current command line to compile Rust solutions is rustc --edition=2018 -O -C link-args=/STACK:268435456 --cfg ONLINE_JUDGE %1

rng_58 it would be great to upgrade version of Rust in Atcoder to 1.35.0 as in Codeforces. The current version (1.15.0), is practically useless and the language has evolved a lot since that.

I modified your code and added a reader field for Scanner

pub struct Scanner<U: Sized + Read> {
    pub buffer: Vec<String>,
    pub reader: U,
}
impl<U: Sized + Read> Scanner<U> {
    pub fn next<T: std::str::FromStr>(&mut self) -> T {
        loop {
            if let Some(token) = self.buffer.pop() {
                return token.parse().ok().expect("Failed parse");
            }
            let mut input = String::new();
            self.reader.read_to_string(&mut input).expect("Failed read");
            self.buffer = input.split_whitespace().rev().map(String::from).collect();
        }
    }

    pub fn new(reader: U) -> Self {
        return Scanner {
            buffer: vec![],
            reader,
        };
    }
}

And my test for p71a looks like

#[test]
    fn test_solution_of_p71a() {
        let mut input_file = BufReader::new(
            "4
word
localization
internationalization
pneumonoultramicroscopicsilicovolcanoconiosis
"
            .as_bytes(),
        );
        let mut out_file = BufWriter::new(Vec::new());
        solution_of_p71a(&mut input_file, &mut out_file);

        assert_eq!(
            "word
l10n
i18n
p43s
",
            String::from_utf8(out_file.into_inner().unwrap())
                .unwrap()
                .as_str()
        );
    }

The stdin can be replaced with a string reader, so easier to test

Would it be possible to add itertools to the available crates when compiling? It's pretty much a must-have, especially when writing algorithms.

Anyone uses Rust to solve SGU problems? My solutions in Rust even fail at the simplest ones, e.g., SGU 118 (Wrong answer on test 2). I compared my code with others' in C/C++ but couldn't find any substantial differences. My code:

// The IO part removed for brevity.

fn dr(x: u32) -> u32 {
    if x == 0 {
        // The digital root of 0 should be 0. Some code posted online omit this condition. Anyway,
        // it doesn't seem to make a difference.
        0
    } else {
        let d = x % 9;
        if d == 0 {
            9
        } else {
            d
        }
    }
}

fn digital_root(a: Vec<u32>) -> u32 {
    dr(
        a
        .iter()
        .scan(1, |p, &x| {
            let x = dr(x);
            *p = dr((*p) * x);
            Some(*p)
        })
        .sum()
    )
}

fn solve<B: BufRead, W: Write>(mut scan: Scanner<B>, mut w: W) {
    let k: usize = scan.token();
    for _ in 0..k {
        let n: usize = scan.token();
        let mut a = Vec::with_capacity(n);
        for _ in 0..n {
            let x: u32 = scan.token();
            a.push(x);
        }
        writeln!(w, "{}", digital_root(a)).expect("failed write");
        w.flush().expect("failed flush"); // not necessary?
    }
}

Could anyone take a look? Thanks.

[submission:https://codeforces.me/contest/793/submission/77476009]

Byte by byte reading using macros.

input! {
    n: usize,
    v: [i32; n],
}

Reads n and Vec<i32> of size n. That's all what you need to write to read an input.

MikeMirzayanov, can codeforces add proconio crate for rust just like what atcoder does? This will be useful for competitive programming in rust.

When I solved this problem, my optimal program in Rust fails because of TLE.

I tried fast I/O from here, and found that fast writing save more time than fast reading, so I suggest to use write!() instead of println!() because it's faster. Use it this way:

// Run this once in start of main
let stdout = std::io::stdout();
let mut writer = std::io::BufWriter::new(stdout.lock());

// Use this everytime you need to print
writeln!(writer, "{}", result).unwrap();

My solution with println!() works more than 1000ms and gets TLE, but the same solution with write!() works 171ms.

Also, when I added the fast read from this comment, I get 140ms instead of 171ms.

How do you deal with random values for several tasks like maintaining treaps, or just randomized solutions?

Any insights about Rust-vs-C++ performance from people who've tried it out in programming contests?

As far as I know, in theory either can happen: Rust can outperform C++ in some aspects (based on the compiler having better understanding of lifetimes, ranges, etc.), but can also be behind in others (e.g., in case one uses array indices extensively and the compiler can't optimize away the boundary checks). Also the differences can stem from different standard library algorithms: Rust's BTreeMap B-Tree vs. C++'s std::map red-black tree (usually).

But I'm curious whether anyone could share real-world, non-synthetic data, e.g., from solutions with segment trees, complex DP, etc.?

Cool. As a Rust fan, I'm really thankful for this blog. By the way, I have a question.

How to write interactive problems using Rust

I had this question but I couldn't get any response from the community. If anyone knows, please help https://codeforces.me/blog/entry/109692