Day 13 Code

use std::env;
use std::io::{self};
use std::collections::HashSet;

extern crate regex;
use regex::Regex;

use point2d::point2d::Point2D;

enum Fold {
    AlongX(i64),
    AlongY(i64)
}
impl From<&str> for Fold {
    fn from(s: &str) -> Self {
        let re = Regex::new(r"fold along ([xy])=(\d+)").unwrap();
        let matches = re.captures(s).unwrap();
        match &matches[1] {
            "x" => Self::AlongX(matches[2].parse().unwrap()),
            "y" => Self::AlongY(matches[2].parse().unwrap()),
            other => panic!("Unknown fold type: {}", other),
        }
    }
}

fn map_extents(map: &HashSet<Point2D>) -> (i64,i64,i64,i64) {
    let xmin = &map.iter().map(|&pt| pt.x).min().unwrap();
    let ymin = &map.iter().map(|&pt| pt.y).min().unwrap();
    let xmax = &map.iter().map(|&pt| pt.x).max().unwrap();
    let ymax = &map.iter().map(|&pt| pt.y).max().unwrap();
    (*xmin,*ymin,*xmax,*ymax)
}

fn solve(input: &str) -> io::Result<()> {
    // Input
    let input_str = std::fs::read_to_string(input).unwrap();
    let input_str = input_str.trim();
    let input: Vec<_> = input_str.split("\n\n").collect();

    let initial_points: Vec<_> = input[0].split("\n").collect();
    let folds: Vec<_> = input[1].split("\n").map(Fold::from).collect();

    // Build initial image
    let mut image: HashSet<Point2D> = HashSet::new();
    let re = Regex::new(r"(\d+),(\d+)").unwrap();
    for point in initial_points {
        let matches = re.captures(&point).unwrap();
        let (x,y) = (matches[1].parse().unwrap(),matches[2].parse().unwrap());
        image.insert(Point2D{x: x, y: y});
    }

    // Process folds
    let (_,_,mut xmax,mut ymax) = map_extents(&image);
    for (i,fold) in folds.iter().enumerate() {

        // Part 1
        if i == 1 {
            let part1 = image.iter().filter(|&pt| pt.x <= xmax && pt.y <= ymax).count();
            println!("Part 1: {}", part1); // 743
        }

        match &fold {
            Fold::AlongX(cut) => {
                for y in 0..=ymax {
                    for x in *cut..=xmax {
                        let pt = Point2D { x: x, y: y };
                        let newpt = Point2D { x: 2*cut-x, y };
                        if image.contains(&pt) { image.insert(newpt); }
                    }
                }
                xmax = *cut;
            },
            Fold::AlongY(cut) => {
                for y in *cut..=ymax {
                    for x in 0..=xmax {
                        let pt = Point2D { x: x, y: y };
                        let newpt = Point2D { x: x, y: 2*cut-y };
                        if image.contains(&pt) { image.insert(newpt); }
                    }
                }
                ymax = *cut;
            },
        }
    }

    println!("Part 2:"); // RCPLAKHL
    for y in 0..=ymax {
        for x in 0..=xmax {
            match image.contains(&Point2D { x: x, y: y }) {
                true => { print!("█"); },
                _    => { print!(" "); },
            }
        }
        println!();
    }

    Ok(())
}

fn main() {
    let args: Vec<String> = env::args().collect();
    let filename = &args[1];
    solve(&filename).unwrap();
}