Post: Advent of code day 19

posts/adventofcode/2017/19-a-series-of-tubes.md

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+---
+title: "A Series of Tubes — Rust — #adventofcode Day 19"
+description: "In which I give Rust another try."
+slug: day-19
+date: 2017-12-24T18:15:28+00:00
+tags:
+- Technology
+- Learning
+- Advent of Code
+- Rust
+series: aoc2017
+---
+
+[Today's challenge](http://adventofcode.com/2017/day/19)
+
+[→ Full code on GitHub](https://github.com/jezcope/aoc2017/blob/master/19-a-series-of-tubes.rs) asks us to help a network packet find its way.
+
+!!! commentary
+    Today's challenge was fairly straightforward, following an [ASCII art](http://en.wikipedia.org/wiki/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.
+
+```rust
+use std::io;
+use std::io::BufRead;
+
+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[0].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);
+}
+```