adventofcode/day05/src/main.rs

use std::error;
use std::fs::File;
use std::io::BufRead;
use std::io::BufReader;

use regex::Regex;

fn main() -> Result<(), Box<dyn error::Error>> {
	let f = File::open("input.txt")?;
	let reader = BufReader::new(f);

	let mut lines = reader.lines();

	let mut items: Vec<Vec<&str>> = Vec::new();

	// read the initial state
	let mut init_lines: Vec<String> = vec![];
	while let Some(Ok(line)) = lines.next() {
		if line == "" {
			break;
		}
		init_lines.push(line);
	}

	init_lines.reverse();
	let mut count = 0;
	for (i, line) in init_lines.iter().enumerate() {
		// init the items with the right amount of Vecs
		if i == 0 {
			count = line.split_whitespace().count();
			for _ in 0..count {
				items.push(vec![]);
			}
			continue;
		}

		// add the items to the vecs
		// let line_iter = line.chars();
		for i in 0..count {
			let item = &line[(i * 4 + 1)..(i * 4 + 2)];
			if item == " " {
				continue;
			}
			items[i].push(&item);
		}
	}

	// read the movements
	let re = Regex::new(r"^move (\d+) from (\d+) to (\d+)$")?;
	while let Some(Ok(line)) = lines.next() {
		// println!("{:?}", re.captures(&line));
		// println!("{:?}", items);
		let cap: Vec<usize> = re.captures(&line).ok_or("Could not match line")?.iter().skip(1).map(|x| x.unwrap().as_str().parse().unwrap()).collect();
		let mut items_to_move = vec![];
		for _ in 0..cap[0] {
			let item = items[cap[1] - 1].pop().ok_or("Found a broken match")?;
			items_to_move.push(item);
		}

		for item in items_to_move.iter().rev() {
			items[cap[2] - 1].push(item);
		}
	}

    // output the result (top of each item-stack i.e. end of the Vec)
	// println!("{:?}", items);
    println!("{}", items.iter().map(|v| String::from(*v.iter().last().unwrap())).collect::<Vec<_>>().join(""));
    Ok(())
}