# A Series of Tubes — Rust — #adventofcode Day 19

Date:

Series

This post is part of the series Advent of Code 2017

Today’s challenge asks us to help a network packet find its way.

→ Full code on GitHub

!!! commentary Today’s challenge was fairly straightforward, following an ASCII art path, so I thought I’d give Rust another try. I’m a bit behind on the blog posts, so I’m presenting the code below without any further commentary. I’m not really convinced this is good idiomatic Rust, and it was interesting turning a set of strings into a 2D array of characters because there are both `u8` (byte) and `char` types to deal with.

``````use std::io;

const ALPHA: &'static str = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

fn change_direction(dia: &Vec<Vec<u8>>, x: usize, y: usize, dx: &mut i32, dy: &mut i32) {
assert_eq!(dia[x][y], b'+');

if dx.abs() == 1 {
*dx = 0;
if y + 1 < dia[x].len() && (dia[x][y + 1] == b'-' || ALPHA.contains(dia[x][y + 1] as char)) {
*dy = 1;
} else if dia[x][y - 1] == b'-' || ALPHA.contains(dia[x][y - 1] as char) {
*dy = -1;
} else {
panic!("Huh? {} {}", dia[x][y+1] as char, dia[x][y-1] as char);
}
} else {
*dy = 0;
if x + 1 < dia.len() && (dia[x + 1][y] == b'|' || ALPHA.contains(dia[x + 1][y] as char)) {
*dx = 1;
} else if dia[x - 1][y] == b'|' || ALPHA.contains(dia[x - 1][y] as char) {
*dx = -1;
} else {
panic!("Huh?");
}
}
}

fn follow_route(dia: Vec<Vec<u8>>) -> (String, i32) {
let mut x: i32 = 0;
let mut y: i32;
let mut dx: i32 = 1;
let mut dy: i32 = 0;
let mut result = String::new();
let mut steps = 1;

match dia.iter().position(|x| *x == b'|') {
Some(i) => y = i as i32,
None => panic!("Could not find '|' in first row"),
}

loop {
x += dx;
y += dy;
match dia[x as usize][y as usize] {
b'A'...b'Z' => result.push(dia[x as usize][y as usize] as char),
b'+' => change_direction(&dia, x as usize, y as usize, &mut dx, &mut dy),
b' ' => return (result, steps),
_ => (),
}
steps += 1;
}
}

fn main() {
let stdin = io::stdin();
let lines: Vec<Vec<u8>> = stdin.lock().lines()
.map(|l| l.unwrap().into_bytes())
.collect();

let result = follow_route(lines);
println!("Route: {}", result.0);
println!("Steps: {}", result.1);
}
``````

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