# What I learned by solving 50 Advent of Code challenges in Rust

Luciano Mammino (@loige)

2023-02-15

# What I learned by solving 50 Advent of Code challenges in Rust

Luciano Mammino (@loige)

2023-02-15

# What I learned by solving 50 Advent of Code challenges in Rust

Luciano Mammino (@loige)

2023-02-15

😅

👋 I'm Luciano (🇮🇹🍕🍝🤌)

👨‍💻 Senior Architect @ fourTheorem

📔 Co-Author of Node.js Design Patterns  👉

Let's connect!

loige.co (blog)

@loige (twitter)

loige (twitch)

lmammino (github)

Grab the slides

# Always re-imagining

### We are a pioneering technology consultancy focused on AWS and serverless

✉️ Reach out to us at  hello@fourTheorem.com

😇 We are always looking for talent: fth.link/careers

awsbites.com podcast

# Why am I learning Rust 🦀

Full-stack Web Developer turning Cloud Architect

Experience with dynamic scripting languages (JavaScript, Python, Php)

Looked into Go for performance-sensitive applications

Rust seemed like the natural next step

... and it's fun!

# How it is going

``````error[E0382]: borrow of moved value: `v`
--> src/main.rs:6:19
|
4 |     let v = vec![2, 3, 5, 7, 11, 13, 17];
|         - move occurs because `v` has type `Vec<i32>`, which does not implement the `Copy` trait
5 |     hold_my_vec(v);
|                 - value moved here
6 |     let element = v.get(3);
|                   ^^^^^^^^ value borrowed here after move
|``````
``````#[stable(feature = "future_poll_fn", since = "1.64.0")]
impl<T, F> Future for PollFn<F>
where
F: FnMut(&mut Context<'_>) -> Poll<T>,
{
type Output = T;

fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<T> {
// SAFETY: We are not moving out of the pinned field.
(unsafe { &mut self.get_unchecked_mut().f })(cx)
}
}``````

# How it started -> How it is going

2019: Ported some JS code to Rust (resulted in jwtinfo)

2020-2022: Live streamed solving Advent of Code in Rust

+ some other small side-projects and coding challenges

Nothing "production ready" as of today 🤷

Excited about Serverless Rust on AWS

# Advent of Code . com

``````Valve NV has flow rate=5; tunnels lead to valves ZV, CG, YB, HX, OY
Valve NU has flow rate=6; tunnels lead to valves DA, MA, OA, DK
Valve VU has flow rate=0; tunnels lead to valves PS, FX
Valve JW has flow rate=0; tunnels lead to valves AA, MD
Valve RI has flow rate=0; tunnels lead to valves OY, DG
Valve DG has flow rate=9; tunnels lead to valves TG, RI, DF, EV, KW
Valve PH has flow rate=7; tunnels lead to valves KW, OW, LT, LZ
Valve KZ has flow rate=12; tunnels lead to valves ET, QV, CK, MS
Valve IX has flow rate=0; tunnels lead to valves TS, DO
Valve MS has flow rate=0; tunnels lead to valves LZ, KZ
Valve IL has flow rate=0; tunnels lead to valves DO, ET
Valve EJ has flow rate=20; tunnels lead to valves AV, JY
Valve DK has flow rate=0; tunnels lead to valves NU, CG
Valve YB has flow rate=0; tunnels lead to valves NV, PS
Valve OA has flow rate=0; tunnels lead to valves YA, NU
Valve DA has flow rate=0; tunnels lead to valves NU, RG
Valve KO has flow rate=0; tunnels lead to valves AA, TG
Valve RG has flow rate=4; tunnels lead to valves DF, DA, ZV, MD, LB
Valve MA has flow rate=0; tunnels lead to valves AA, NU
Valve OW has flow rate=0; tunnels lead to valves DO, PH
Valve KW has flow rate=0; tunnels lead to valves DG, PH
Valve DO has flow rate=14; tunnels lead to valves IX, IL, CZ, OW
Valve DF has flow rate=0; tunnels lead to valves RG, DG
Valve TG has flow rate=0; tunnels lead to valves DG, KO
Valve LB has flow rate=0; tunnels lead to valves RG, FX
Valve HX has flow rate=0; tunnels lead to valves AA, NV
Valve GB has flow rate=0; tunnels lead to valves AV, XK
Valve CG has flow rate=0; tunnels lead to valves DK, NV
Valve LT has flow rate=0; tunnels lead to valves AO, PH
Valve FX has flow rate=23; tunnels lead to valves LB, HY, VU
Valve ET has flow rate=0; tunnels lead to valves IL, KZ
Valve CK has flow rate=0; tunnels lead to valves UX, KZ
Valve LZ has flow rate=0; tunnels lead to valves PH, MS
Valve YA has flow rate=17; tunnels lead to valves JY, OA
Valve TS has flow rate=0; tunnels lead to valves NO, IX
Valve NO has flow rate=8; tunnel leads to valve TS
Valve XK has flow rate=24; tunnel leads to valve GB``````

1. Read & understand the puzzle

2. Parse the input

3. Write some code

4. Find solution

5. Submit your solution (unlocks part 2)

6. Repeat from point 1 for part 2

# Iterator combinators

y2022 - Day 1: Calorie Counting

``````

1000
2000
3000

4000

5000
6000

7000
8000
9000

10000``````

sum

sum

sum

sum

sum

max

`6000`
`4000`
`11000`
`24000`
`10000`
`24000`

Classic noob approach

``````fn classic(input: &str) -> u64 {
let mut max = 0;
let batches = input.split("\n\n");
for batch in batches {
let lines = batch.lines();
let mut total = 0;
for line in lines {
let value = line.parse::<u64>().unwrap();
total += value;
}
if total > max {
max = total;
}
}
max
}``````

Combinators approach

``````fn combinators(input: &str) -> u64 {
input
.split("\n\n")
.map(|batch| {
batch
.lines()
.map(|line| line.parse::<u64>().unwrap())
.sum::<u64>()
})
.max()
.unwrap()
}``````

Nice, but the classic noob version must be much faster, right? 🤔

⚡️ NOT REALLY!

Yeah, but I am sure that
iterator combinators are
not always flexible enough, right? 🤔

y2022 Day 1: Calorie Counting (part 2)

``````

1000
2000
3000

4000

5000
6000

7000
8000
9000

10000``````

sum

sum

sum

sum

sum

top 3

`6000`
`4000`
`11000`
`24000`
`10000`
`24000`
`11000`
`10000`

sum

`45000`
``````fn combinators(input: &str) -> u64 {
input
.split("\n\n")
.map(|batch| {
batch
.lines()
.map(|line| line.parse::<u64>().unwrap())
.sum::<u64>()
})
.sort_descending()
.take(3)
.sum()
}``````
``````fn combinators(input: &str) -> u64 {
input
.split("\n\n")
.map(|batch| {
batch
.lines()
.map(|line| line.parse::<u64>().unwrap())
.sum::<u64>()
})
.sort_descending()
.take(3)
.sum()
}``````

🤷

But iterator combinators can be "extended" 🤫

``\$ cargo add itertools``
``````use itertools::Itertools;

fn combinators(input: &str) -> u64 {
input
.split("\n\n")
.map(|batch| {
batch
.lines()
.map(|line| line.parse::<u64>().unwrap())
.sum::<u64>()
})
.sorted()
.rev()
.take(3)
.sum()
}``````
``````use itertools::Itertools;

fn combinators(input: &str) -> u64 {
input
.split("\n\n")
.map(|batch| {
batch
.lines()
.map(|line| line.parse::<u64>().unwrap())
.sum::<u64>()
})
.sorted()
.rev()
.take(3)
.sum()
}``````

🤩

added by itertools

But... Do we really want to sort? 😕

💡IDEA:

Consume the iterator and, as you go, keep the current top 3 in a vec...

💡IDEA:

Consume the iterator and, as you go, keep the current top 3 in a vec...

```100
22
44
1
120```
`top3 = []`
```100
22
44
1
120```
`top3 = []`

👉

💡IDEA:

Consume the iterator and, as you go, keep the current top 3 in a vec...

```100
22
44
1
120```
`top3 = [100]`

👉

💡IDEA:

Consume the iterator and, as you go, keep the current top 3 in a vec...

```100
22
44
1
120```
`top3 = [100]`

👉

💡IDEA:

Consume the iterator and, as you go, keep the current top 3 in a vec...

```100
22
44
1
120```
`top3 = [100,22]`

👉

💡IDEA:

Consume the iterator and, as you go, keep the current top 3 in a vec...

```100
22
44
1
120```
`top3 = [100,22]`

👉

💡IDEA:

Consume the iterator and, as you go, keep the current top 3 in a vec...

```100
22
44
1
120```
`top3 = [100,44,22]`

👉

💡IDEA:

Consume the iterator and, as you go, keep the current top 3 in a vec...

```100
22
44
1
120```
`top3 = [100,44,22]`

👉

💡IDEA:

Consume the iterator and, as you go, keep the current top 3 in a vec...

```100
22
44
1
120```
`top3 = [100,44,22]`

👉

💡IDEA:

Consume the iterator and, as you go, keep the current top 3 in a vec...

```100
22
44
1
120```
`top3 = [120,100,44]`

👉

💡IDEA:

Consume the iterator and, as you go, keep the current top 3 in a vec...

```100
22
44
1
120```
`top3 = [120,100,44]`

This is O(n*m) vs sorting O(n*logn) ⚡️

* indulge me and let's ignore we could have used radix sort here...

** O(n) for very small m, top100 would be expensive!

💡IDEA:

Consume the iterator and, as you go, keep the current top 3 in a vec...

``````trait TopN {
fn top_n(self, n: usize) -> Vec<u64>;
}``````

That's what we want for now, but can it be more "generic"? 🧐

``````trait TopN<T> {
fn top_n(self, n: usize) -> Vec<T>;
}``````

Makes the trait "generic" over any type T

T is used as part of the return type of the function

That's a cool trait indeed... but I am sure we cannot implement it for "all" iterators, right?! 🤷

Of course, we can! 💪

It's called a "blanket implementation".

``````impl<T, U: Iterator<Item = T>> TopN<T> for U {
fn top_n(self, n: usize) -> Vec<T> {
// TODO:
unimplemented!();
}
}``````

When you implement traits with generics, you can restrict for which types the implementation is relevant

All types U that implements the Iterator trait producing Items of type T

We implement TopN<T> for all types U (iterators producing T)!

``````impl<T, U: Iterator<Item = T>> TopN<T> for U {
fn top_n(self, n: usize) -> Vec<T> {
let mut top = Vec::with_capacity(n);
for value in self {
for i in 0..n {
if let Some(top_value) = top.get(i) {
if value > *top_value {
top[i..].rotate_right(1);
top[i] = value;
break;
}
} else {
top.push(value);
break;
}
}
}
top
}
}``````
``````impl<T, U: Iterator<Item = T>> TopN<T> for U {
fn top_n(self, n: usize) -> Vec<T> {
let mut top = Vec::with_capacity(n);
for value in self {
for i in 0..n {
if let Some(top_value) = top.get(i) {
if value > *top_value {
top[i..].rotate_right(1);
top[i] = value;
break;
}
} else {
top.push(value);
break;
}
}
}
top
}
}``````
``````impl<T: PartialOrd, U: Iterator<Item = T>> TopN<T> for U {
fn top_n(self, n: usize) -> Vec<T> {
let mut top = Vec::with_capacity(n);
for value in self {
for i in 0..n {
if let Some(top_value) = top.get(i) {
if value > *top_value {
top[i..].rotate_right(1);
top[i] = value;
break;
}
} else {
top.push(value);
break;
}
}
}
top
}
}``````

Restricting T only to types that can be compared!

👍

``````fn combinators_no_sort(input: &str) -> u64 {
input
.split("\n\n")
.map(|batch| {
batch
.lines()
.map(|line| line.parse::<u64>().unwrap())
.sum::<u64>()
})
.top_n(3)
.iter()
.sum()
}``````
``````fn combinators_no_sort(input: &str) -> u64 {
input
.split("\n\n")
.map(|batch| {
batch
.lines()
.map(|line| line.parse::<u64>().unwrap())
.sum::<u64>()
})
.top_n(3)
.iter()
.sum()
}``````

😍

OMG, we added this!

OK, but you used a Vec there...
I heard rustaceans don't like unnecessary allocations, right?! 🤷

``````trait Top<T> {
fn top(self, n: usize) -> Vec<T>;
}

impl<T: PartialOrd, U: Iterator<Item = T>> Top<T> for U {
fn top(self, n: usize) -> Vec<T> {
let mut top = Vec::with_capacity(n);
// ...
top
}
}``````

We want to replace these with an array...

``````trait Top<T> {
fn top(self, n: usize) -> [T;n];
}

impl<T: PartialOrd, U: Iterator<Item = T>> Top<T> for U {
fn top(self, n: usize) -> [T;n] {
let mut top = [T;n];
// ...
top
}
}``````
``````trait Top<T> {
fn top<const N: usize>(self) -> [T; N];
}

impl<T: PartialOrd, U: Iterator<Item = T>> Top<T> for U {
fn top<const N: usize>(self) -> [T; N] {
let mut top = [T;N];
// ...
top
}
}``````

const generics syntax

``````trait Top<T> {
fn top<const N: usize>(self) -> [T; N];
}

impl<T: PartialOrd, U: Iterator<Item = T>> Top<T> for U {
fn top<const N: usize>(self) -> [T; N] {
let mut top = [T;N];
// ...
top
}
}``````
``````trait Top<T> {
fn top<const N: usize>(self) -> [T; N];
}

impl<T: PartialOrd, U: Iterator<Item = T>> Top<T> for U {
fn top<const N: usize>(self) -> [T; N] {
let mut top = [Default::default(); N];
// ...
top
}
}``````
``````trait Top<T> {
fn top<const N: usize>(self) -> [T; N];
}

impl<T: Default + Copy + PartialOrd, U: Iterator<Item = T>> Top<T> for U {
fn top<const N: usize>(self) -> [T; N] {
let mut top = [Default::default(); N];
// ...
top
}
}``````
``````trait Top<T> {
fn top<const N: usize>(self) -> [T; N];
}

impl<T: Default + Copy + PartialOrd, U: Iterator<Item = T>> Top<T> for U {
fn top<const N: usize>(self) -> [T; N] {
let mut top = [Default::default(); N];
// ...
top
}
}``````

Do we really need this?

``````trait Top<T> {
fn top<const N: usize>(self) -> [T; N];
}

impl<T: Default + PartialOrd, U: Iterator<Item = T>> Top<T> for U {
fn top<const N: usize>(self) -> [T; N] {
let mut top = core::array::from_fn(|_| Default::default());
// ...
top
}
}``````

Allows us to avoid Copy

``````trait Top<T> {
fn top<const N: usize>(self) -> [T; N];
}

impl<T: Default + PartialOrd, U: Iterator<Item = T>> Top<T> for U {
fn top<const N: usize>(self) -> [T; N] {
let mut top = core::array::from_fn(|_| Default::default());
// ...
top
}
}``````

Note: This works for now, but it's not a perfect solution 😥

(e.g. what if there are fewer than N items?)

``````fn combinators_no_sort_const(input: &str) -> u64 {
input
.split("\n\n")
.map(|batch| {
batch
.lines()
.map(|line| line.parse::<u64>().unwrap())
.sum::<u64>()
})
.top::<3>()
.iter()
.sum()
}``````
``````fn combinators_no_sort_const(input: &str) -> u64 {
input
.split("\n\n")
.map(|batch| {
batch
.lines()
.map(|line| line.parse::<u64>().unwrap())
.sum::<u64>()
})
.top::<3>()
.iter()
.sum()
}``````

Slightly different syntax 🐟

Phew... we did it!

😮‍💨

Which one do you think is faster? 🧐

Itertools

no_sort_vec

no_sort_array

1.

2.

3.

Which one do you think is faster? 🧐

Itertools

no_sort_vec

no_sort_array

1.

2.

3.

37.517 µs

33.284 µs

32.957 µs

BTW, cargo bench is awesome!

⭐️

But let's talk more about
const generics, what else can you do with them?

y2020 - Day 17: Conway Cubes

``````struct Point<const D: usize>([i32; D]);

fn make_2d_point(x: i32, y: i32) -> Point<2> {
Point([x, y])
}

fn make_3d_point(x: i32, y: i32, z: i32) -> Point<3> {
Point([x, y, z])
}

fn make_4d_point(x: i32, y: i32, z: i32, w: i32) -> Point<4> {
Point([x, y, z, w])
}``````

y2020 - Day 17: Conway Cubes

``````fn some_func() {
// ...
let p5d = Point([1, 2, 3, 4, 5]);
// ...
}``````

No need to specify the type, Rust will infer Point<5> based on the length of the passed array!

y2021 - Day 25: Sea Cucumber

``````v...>>.vv>
.vv>>.vv..
>>.>v>...v
>>v>>.>.v.
v>v.vv.v..
>.>>..v...
.vv..>.>v.
v.v..>>v.v
....v..v.>``````

Sometimes you have to handle grids of variable sizes.

README example (10x9)

y2021 - Day 25: Sea Cucumber

``````.v.v.v>...>vv>v>>>.v>..v>.v.>.>v>.v.v.>>v...>.>....>.>vv>>>.....>>...v.>>v..>..vvv.>v...vv...>..>....>.>.>.>vvv....>..vv>v....>v...>>....v.
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v.v..vvv>...>v......v....>..>>>.....v>v>>>..v.v..vv.>.>>>>.>.v.>....v.>.>v>vv>vv>v..>.>.v.v>.....>..v>>v...v.....v...v.v.vv>>........v.>.v>
.v>>...>>v>.>...v.>>>....>v>>v.>.v.>>v.v>.>>...>.v.v...vv>v....v>v..>>.>v>.>..>vv.v>>.>..v>>v...>v>>>..v..>v>vv.vv>............>v..>vv.v.vv
>.....>vv.>...v>vvvv>vvv..vvv>.v.>...>v..vv>vv.>>>.v..v>v.>..vv.v.>>v....v...v.....>.v.>.>..>.v>..>v..>>>>>>>v..vv>.v.v>v.v>..>....>>>v>.vv
v.>.v>v.v>...>>>..v>..>>.>..v.v....>.>....v.>..>>>.>v.>.>.>vv..>.>...v.>.....>vv>.>..vv.vvv.>>.vv.>.....vvvv>..v.>.>>v..v..>.>>.>...v>>v..>
v..v>v>..vvv>...v..>.>>...v.v..v..>v..>>.>>.v..>>v...v.vv..v..>...v...v....>v.v.v.v.>.v>vvv.v.v>...>v>.>..>v.v>v>v..v..>>>>...>v.....v.>..v
v>v..v..>..v>.....>>>.v..>v>v..>..>v>...v..>....v...v>>vv.....v.vv...v>....v>..v>>.v.>.>>..>v>..>>>vv.>>>...>...v>vv>v>...>..v.v..>.....>>.
vv..>>v..>>>.>...v..v.>v>..v.>>>>>v..v>v>..>v>>>v.....v..>.>.>>vv.v....v.....>v......>.>vv..vv>.vv..vv...vv.v...>.v..>.>.v>v...v>..vv...>vv
.>...vv>>>.v.....v....>.v......vvvv>.>..>vv>v..vv..>v>>.>v.v>.v>v.vvvvv.v>v......v.>v>vv..>v..>vv.v.v.vvv..>.>.>>v.v.......>vv..v.vv>.>.v..
....v...v.>.v>>>v.>.....>>v>..v>.v.>.v.>..>v.>vv>>vv.>........v..>v>.v>>v>>v.>....>.>...>.>.v.......v....v>vvv..v>..>..v>....v...>.v.>.v...
..vvv.v>.>...>>.vvv>...v...>..>..>...v>v>..>>.vv....>.v.v.>.v>vv.>>v..v>.v.v..v.>.>>.v.....>.v...v>.....v....v.v.v.>>....v.v>>>.......>vv.v
...v>v>..v.v.v...>v>.vvv.vv..>..v.>v.>vv.>.>>..v....>.v.....>.v>..>..v>>vv..vv.>....v>>.v>...>.>vv....v>>.>>v>....>.v.v>v>>>>...>....>.>..v
.>>..v.>v..>>>v.v.v>>...>>v...v>....>.v>>...v.>.v.>...v>>vv.vvv>v....v>.v.>v......v.v.>>.>v...v...>vv.v.....>...>.>..vv.v..>..>.v>..>.v>.vv
>..>.>.>>.v.v.>.v.vvv....>.v>v.v..v.v...>...vv..>>.>..>>>...v>.>.v..v.>>.......v.....>.v>vv.>.v..vv>>>>>>v...vvv..vvv>>>.v.>.v..v.v>v>v>..>
v..>.v.vv>>vvvvv.....v>>v...vv....v>.>>v.v.>.>>v.vv....vv..v.>>.v.v.>v>....>....v.v>>>.>v.v.>v>v.v.v..>.>v>v......v.v>...>v.vvv...v>...vv..
>>vv.....v...v......>v.v..v>..v.v>..>>>.>>..>v>.v>>>.>v..>>>>v.>..vvvv.v>...v..vv.>.>v....>v.>>.....v>v....v..>.>.v>v.>.>.>v.v..>v.........``````

Sometimes you have to handle grids of variable sizes.

Actual input (139x137)

y2021 - Day 25: Sea Cucumber

``````struct Grid<const W: usize, const H: usize> {
cells: [[Option<Cell>; W]; H],
}``````

You can use const generics to define a matrix
with configurable dimensions

y2021 - Day 25: Sea Cucumber

``````struct Grid<const W: usize, const H: usize> {
cells: [[Option<Cell>; W]; H],
}

pub fn test_readme(input: &str) -> usize {
let mut grid1: Grid<10, 9> = input.parse().unwrap();
// ...
}

pub fn part1(input: &str) -> usize {
let mut grid1: Grid<139, 137> = input.parse().unwrap();
// ...
}``````

# Parsing

(Ergo, extracting data from text)

y2020 - Day 14: Docking Data

``````mask = 000000000000000000000000000000X1001X
mem[42] = 100
mask = 00000000000000000000000000000000X0XX
mem[26] = 1
...``````
``````enum Instr {
Mask(String),
Mem(u64, u64),
}``````
``````use std::str::FromStr;

impl FromStr for Instr {
type Err = String;

fn from_str(s: &str) -> Result<Self, Self::Err> {
if s.starts_with("mask") {
Ok(Instr::Mask(s[7..].to_string()))
} else if s.starts_with("mem") {
let addr_value = &mut s[4..].split("] = ");
let addr: u64 = addr_value.next().unwrap().parse().unwrap();
let value: u64 = addr_value.next().unwrap().parse().unwrap();
Ok(Instr::Mem(addr, value))
} else {
Err(format!("Invalid line found: {s}"))
}
}
}``````
``````let mask: Instr = "mask = 00000000000000X1001X".parse().unwrap();
assert_eq!(mask, Instr::Mask("00000000000000X1001X".to_string()));

let mem: Instr = "mem[42] = 100".parse().unwrap();
assert_eq!(mem, Instr::Mem(42, 100));``````
``````let mask: Instr = "mask = 00000000000000X1001X".parse().unwrap();
assert_eq!(mask, Instr::Mask("00000000000000X1001X".to_string()));

let mem: Instr = "mem[42] = 100".parse().unwrap();
assert_eq!(mem, Instr::Mem(42, 100));``````

Implementing the FromStr trait, will make the parse() method available!

oops, I did it again:
unnecessary allocations! 🤷

Why don't you just take a slice from the input rather than allocating a String?

``````enum Instr<'a> {
Mask(&'a str),
Mem(u64, u64),
}

impl<'a> FromStr for Instr<'a> {
type Err = String;

fn from_str(s: &'a str) -> Result<Self, Self::Err> {
if s.starts_with("mask") {
Ok(Instr::Mask(&s[7..]))
} else if s.starts_with("mem") {
let addr_value = &mut s[4..].split("] = ");
let addr: u64 = addr_value.next().unwrap().parse().unwrap();
let value: u64 = addr_value.next().unwrap().parse().unwrap();
Ok(Instr::Mem(addr, value))
} else {
Err(format!("Invalid line found: {s}"))
}
}
}``````
``````enum Instr<'a> {
Mask(&'a str),
Mem(u64, u64),
}

impl<'a> FromStr for Instr<'a> {
type Err = String;

fn from_str(s: &'a str) -> Result<Self, Self::Err> {
if s.starts_with("mask") {
Ok(Instr::Mask(&s[7..]))
} else if s.starts_with("mem") {
let addr_value = &mut s[4..].split("] = ");
let addr: u64 = addr_value.next().unwrap().parse().unwrap();
let value: u64 = addr_value.next().unwrap().parse().unwrap();
Ok(Instr::Mem(addr, value))
} else {
Err(format!("Invalid line found: {s}"))
}
}
}``````
``````enum Instr<'a> {
Mask(&'a str),
Mem(u64, u64),
}

impl<'a> From<&'a str> for Instr<'a> {
fn from(s: &'a str) -> Self {
if s.starts_with("mask") {
Instr::Mask(&s[7..])
} else if s.starts_with("mem") {
let addr_value = &mut s[4..].split("] = ");
let addr: u64 = addr_value.next().unwrap().parse().unwrap();
let value: u64 = addr_value.next().unwrap().parse().unwrap();
Instr::Mem(addr, value)
} else {
panic!("Invalid line found: {s}")
}
}
}``````
``````enum Instr<'a> {
Mask(&'a str),
Mem(u64, u64),
}

impl<'a> From<&'a str> for Instr<'a> {
fn from(s: &'a str) -> Self {
if s.starts_with("mask") {
Instr::Mask(&s[7..])
} else if s.starts_with("mem") {
let addr_value = &mut s[4..].split("] = ");
let addr: u64 = addr_value.next().unwrap().parse().unwrap();
let value: u64 = addr_value.next().unwrap().parse().unwrap();
Instr::Mem(addr, value)
} else {
panic!("Invalid line found: {s}")
}
}
}``````

This panic gives me anxiety 😰

``````use std::convert::{TryFrom, TryInto};

enum Instr<'a> {
Mask(&'a str),
Mem(u64, u64),
}

impl<'a> TryFrom<&'a str> for Instr<'a> {
type Error = String;

fn try_from(s: &'a str) -> Result<Self, Self::Error> {
if s.starts_with("mask") {
Ok(Instr::Mask(&s[7..]))
} else if s.starts_with("mem") {
let addr_value = &mut s[4..].split("] = ");
let addr: u64 = addr_value.next().unwrap().parse().unwrap();
let value: u64 = addr_value.next().unwrap().parse().unwrap();
Ok(Instr::Mem(addr, value))
} else {
Err(format!("Invalid line found: {s}"))
}
}
}``````
``````let mask: Instr = "mask = 00000000000000X1001X".try_into().unwrap();
assert_eq!(mask, Instr::Mask("00000000000000X1001X"));

let mem: Instr = "mem[42] = 100".try_into().unwrap();
assert_eq!(mem, Instr::Mem(42, 100));``````

Implementing the TryFrom trait, will make the try_into() method available!

y2022 - Day 15: Beacon Exclusion Zone

``````Sensor at x=2, y=18: closest beacon is at x=-2, y=15
Sensor at x=9, y=16: closest beacon is at x=10, y=16
Sensor at x=13, y=2: closest beacon is at x=15, y=3
Sensor at x=12, y=14: closest beacon is at x=10, y=16
...``````
``````struct Pos {
x: i64,
y: i64,
}``````
``````let sensor = Pos {
x: 13,
y: 2,
}``````
``````let beacon = Pos {
x: 15,
y: 3,
}``````

😱

``````use regex::Regex;

fn parse_line_regex(line: &str) -> (Pos, Pos) {
let re = Regex::new(
r"Sensor at x=(?P<x1>[-]?\d+), y=(?P<y1>[-]?\d+): closest beacon is at x=(?P<x2>[-]?\d+), y=(?P<y2>[-]?\d+)",
)
.unwrap();

let captures = re.captures(line).unwrap();
let sensor = Pos {
x: captures["x1"].parse().unwrap(),
y: captures["y1"].parse().unwrap(),
};
let beacon = Pos {
x: captures["x2"].parse().unwrap(),
y: captures["y2"].parse().unwrap(),
};
(sensor, beacon)
}``````
``````use regex::Regex;

fn parse_line_regex(line: &str) -> (Pos, Pos) {
let re = Regex::new(
r"Sensor at x=(?P<x1>[-]?\d+), y=(?P<y1>[-]?\d+): closest beacon is at x=(?P<x2>[-]?\d+), y=(?P<y2>[-]?\d+)",
)
.unwrap();

// ...
(sensor, beacon)
}

pub fn parse_regex(input: &str) -> impl Iterator<Item = (Pos, Pos)> + '_ {
input.lines().map(parse_line_regex)
}``````

Aren't we re-istantiating the Regex over and over? 🤷

How can we initialize the regex globally?

``\$ cargo add lazy_static``
``````#[macro_use]
extern crate lazy_static;
use regex::Regex;

lazy_static! {
static ref LINE_REGEX: Regex = Regex::new(r"Sensor at x=(?P<x1>[-]?\d+), y=(?P<y1>[-]?\d+): closest beacon is at x=(?P<x2>[-]?\d+), y=(?P<y2>[-]?\d+)")
.unwrap();
}

fn parse_line_regex(line: &str) -> (Pos, Pos) {
let captures = LINE_REGEX.captures(line).unwrap();

// ...
(sensor, beacon)
}

pub fn parse_regex(input: &str) -> impl Iterator<Item = (Pos, Pos)> + '_ {
input.lines().map(parse_line_regex)
}``````

🤷 BTW,

should I tell you that when you solve a problem with a Regex... BLAH BLAH BLAH?!

Ok, let's do proper parsing with nom! 💪

``\$ cargo add nom``
``````fn parse_i64(input: &str) -> IResult<&str, i64> {
let (input, sign) = opt(tag("-"))(input)?;
let (input, value) = digit1(input)?;
let mut value = value.parse::<i64>().unwrap();
if sign.is_some() {
value *= -1;
}
Ok((input, value))
}``````
``````fn parse_line(input: &str) -> IResult<&str, (Pos, Pos)> {
let (input, (s_x, s_y, b_x, b_y)) = all_consuming(tuple((
preceded(tag("Sensor at x="), parse_i64),
preceded(tag(", y="), parse_i64),
preceded(tag(": closest beacon is at x="), parse_i64),
preceded(tag(", y="), parse_i64),
)))(input)?;
let p1 = Pos { x: s_x, y: s_y };
let p2 = Pos { x: b_x, y: b_y };
Ok((input, (p1, p2)))
}``````

Which one do you think is faster? 🧐

regex

regex_lazy

nom

1.

2.

3.

Which one do you think is faster? 🧐

regex

regex_lazy

nom

1.

2.

3.

Which one do you think is faster? 🧐

regex

regex_lazy

nom

1.

2.

3.

3063.9 µs

9.3 µs

1.8 µs

⭐️

+170117%

+417%

• The Iterator & the FromIterator traits
• Destructuring with if let Some(x) / while let Some(x)...
• Powerful pattern-matching syntax and the matches!() macro
• Newtype pattern + Deref & DerefMut trait
• The Display & Debug traits
• unreachable!() & todo!() macros
• defaultdict a-la-python using HashMap and the entry API
• Copy On Write (CoW)
• Helper methods of the Result and the Option types

## I would have also loved to tell you about... 🤯

• Started with a very imperative style and ended up with a more functional style
• "if you look back at your code from 2 years ago and you are not ashamed you are not growing"
• Noticed that rust has been improving a lot in these 3 years
• Often needed helpers but they were in nightly (Vec::retain)
• Rust Analyser & Clippy have been suggesting new improvements over time!
• Rust is fantastic for Advent of Code!

## 🦀 In conclusion...

Photo by Nathan Dumlao on Unsplash

# Never stop learning!

Huge thanks to @gbinside, @AlleviTommaso, @giufus
Cover photo by Redaviqui Davilli on Unsplash

TNX

Sorry, I have a contractual obligation to put this here 😛

#### What I learned by solving 50 Advent of Code challenges in Rust - RustNation UK 2023

By Luciano Mammino

# What I learned by solving 50 Advent of Code challenges in Rust - RustNation UK 2023

In 2020 I started to be a bit more serious about learning Rust. After having read a few books and having done some coding challenges, I decided to start live-streaming my attempts to solve Advent of Code challenges using Rust. Fast forward to 2022 I completed 50 challenges and learned a lot about how to use Rust to solve specific programming challenges. In this talk, I’ll be sharing some common tips and tricks that I discovered while live-coding also thanks to the beautiful Rust community that gave me tons of suggestions! Some topics I’ll be covering in this talk: parsing input, data structures, error handling, iterators, performance, allocating and manipulating 2d matrices, etc.

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