AoC2021/src/bin/day13.rs

use std::collections::HashSet;
use std::error::Error;
use std::fs::File;
use std::io::{self, BufRead};
use std::vec::Vec;

enum Fold {
    X(i32),
    Y(i32),
}

fn fold_x(coord: i32, points: &HashSet<(i32, i32)>) -> HashSet<(i32, i32)> {
    let left_points: HashSet<(i32, i32)> = points
        .iter()
        .filter(|(x, _)| x <= &coord)
        .cloned()
        .collect();
    let right_points: HashSet<(i32, i32)> = points
        .difference(&left_points)
        .map(|(x, y)| (coord - (x - coord), y.clone()))
        .collect();

    left_points.union(&right_points).cloned().collect()
}

fn fold_y(coord: i32, points: &HashSet<(i32, i32)>) -> HashSet<(i32, i32)> {
    let below_points: HashSet<(i32, i32)> = points
        .iter()
        .filter(|(_, y)| y <= &coord)
        .cloned()
        .collect();
    let above_points: HashSet<(i32, i32)> = points
        .difference(&below_points)
        .map(|(x, y)| (x.clone(), coord - (y - coord)))
        .collect();

    below_points.union(&above_points).cloned().collect()
}

fn print_points(points: &HashSet<(i32, i32)>) {
    let mut max_x = 0;
    let mut max_y = 0;
    for (x, y) in points.iter() {
        if x > &max_x {
            max_x = *x;
        }
        if y > &max_y {
            max_y = *y;
        }
    }

    for y in 0..max_y + 1 {
        for x in 0..max_x + 1 {
            if points.contains(&(x, y)) {
                print!("#")
            } else {
                print!(".")
            }
        }
        println!("");
    }
}

fn main() -> Result<(), Box<dyn Error>> {
    let file = File::open("inputs/day13.txt")?;
    let mut lines = io::BufReader::new(file).lines();

    let mut points: HashSet<(i32, i32)> = HashSet::new();

    while let Some(Ok(line)) = lines.next() {
        if line == "" {
            break;
        }

        let mut coords = line.split(',').map(|c| -> i32 { c.parse().unwrap() });
        points.insert((coords.next().unwrap(), coords.next().unwrap()));
    }

    let mut folds: Vec<Fold> = Vec::new();
    while let Some(Ok(line)) = lines.next() {
        if line == "" {
            break;
        }

        let mut parts = line.split("=");
        let inst = parts.next().unwrap();
        let coord: i32 = parts.next().unwrap().parse().unwrap();

        match inst {
            "fold along x" => folds.push(Fold::X(coord)),
            "fold along y" => folds.push(Fold::Y(coord)),
            _ => panic!("Unkonwn instruction: {}", inst),
        }
    }

    let mut answer1: Option<usize> = None;
    let mut folded_points = points.clone();
    for fold in folds.iter() {
        match fold {
            Fold::X(x) => folded_points = fold_x(*x, &folded_points),
            Fold::Y(y) => folded_points = fold_y(*y, &folded_points),
        }
        if answer1.is_none() {
            answer1 = Some(folded_points.len());
        }
    }

    println!("Answer1: {}", answer1.unwrap());
    println!("");

    println!("Answer2:");
    print_points(&folded_points);

    Ok(())
}