aoc-2021/d05/src/main.rs

use std::cmp::Ordering;
use std::fmt;
use std::fs;

#[derive(Debug, Default, Clone, Copy, PartialEq, PartialOrd, Eq)]
struct Point(i32, i32);

impl Point {
    fn from_str(input: &str) -> Self {
        let coords: Vec<i32> = input
            .split(",")
            // TODO: propogate this error
            .map(|n| n.parse::<i32>().unwrap())
            .collect();
        // TODO: Check length
        Point(coords[0], coords[1])
    }
}

impl fmt::Display for Point {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "({}, {})", self.0, self.1)
    }
}

impl Ord for Point {
    fn cmp(&self, other: &Self) -> Ordering {
        let x_ordering = self.0.cmp(&other.0);
        if x_ordering == Ordering::Equal {
            self.1.cmp(&other.1)
        } else {
            x_ordering
        }
    }
}

#[derive(Debug, Default, Clone, Copy)]
struct Line(Point, Point);

impl Line {
    fn from_str(input: &str) -> Self {
        // TODO: propagate error
        let parts: Vec<Point> = input.split(" -> ").map(|p| Point::from_str(p)).collect();
        // TODO: Check length
        Line(parts[0], parts[1])
    }

    fn is_horizontal(&self) -> bool {
        self.0 .1 == self.1 .1
    }

    fn is_vertical(&self) -> bool {
        self.0 .0 == self.1 .0
    }

    fn calc_x(&self, y: i32) -> i32 {
        if self.is_vertical() {
            return self.0 .0;
        }
        // (y1 - x1) / (y2 - x2)
        let slope: f64 = (f64::from(self.1 .1) - f64::from(self.0 .1))
            / (f64::from(self.1 .0) - f64::from(self.0 .0));
        let offset = f64::from(self.1 .1) - (f64::from(self.1 .0) * slope);

        ((f64::from(y) - offset) / slope) as i32
    }

    fn calc_y(&self, x: i32) -> i32 {
        // (y1 - x1) / (y2 - x2)
        let slope: f64 = (f64::from(self.1 .1) - f64::from(self.0 .1))
            / (f64::from(self.1 .0) - f64::from(self.0 .0));
        let offset = f64::from(self.1 .1) - (f64::from(self.1 .0) * slope);

        ((f64::from(x) * slope) + offset) as i32
    }

    fn interpolate_line(&self) -> Vec<Point> {
        // Walk along x
        let x_walk = (self.0 .0.min(self.1 .0)..(self.0 .0.max(self.1 .0) + 1))
            .map(|x| Point(x, self.calc_y(x)));
        // Walk along y
        let y_walk = (self.0 .1.min(self.1 .1)..(self.0 .1.max(self.1 .1) + 1))
            .map(|y| Point(self.calc_x(y), y));

        if self.is_horizontal() {
            x_walk.collect()
        } else if self.is_vertical() {
            y_walk.collect()
        } else {
            let mut points: Vec<Point> = x_walk.chain(y_walk).collect();
            points.sort();
            points.dedup();
            points
        }
    }
}

impl fmt::Display for Line {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "<{} -> {}>", self.0, self.1)
    }
}

fn join_points(points: &Vec<Point>) -> String {
    points
        .iter()
        .map(|p| format!("{}", p))
        .collect::<Vec<String>>()
        .join(" -> ")
}

fn join_vec<T: std::fmt::Display>(join_str: &str, v: &Vec<T>) -> String {
    v.iter()
        .map(|p| format!("{}", p))
        .collect::<Vec<String>>()
        .join(join_str)
}

/// Returns the maximum point in a grid bound by the input vector
///
/// # Arguments
///
/// * `points` - A vector of points that should fit in the grid
fn max_point(points: &Vec<Point>) -> Point {
    points.iter().fold(Point(0, 0), |max, point| {
        Point(max.0.max(point.0), max.1.max(point.1))
    })
}

fn part1() {
    let file_contents = fs::read_to_string("input.txt").expect("No input found");
    let lines: Vec<Line> = file_contents
        .lines()
        .map(|l| Line::from_str(l))
        .filter(|l| l.is_horizontal() || l.is_vertical())
        .collect();

    for line in &lines {
        println!("Line is {}", line);
        let line_points: Vec<Point> = line.interpolate_line();
        println!("Full line: {}", join_points(&line_points));
    }

    let all_points = lines
        .iter()
        .map(|line| line.interpolate_line())
        .flatten()
        .collect();
    let grid_max = max_point(&all_points);
    let mut grid: Vec<Vec<i32>> = (0..(grid_max.1 + 1))
        .map(|_| (0..(grid_max.0 + 1)).map(|_| 0).collect::<Vec<i32>>())
        .collect();

    for point in &all_points {
        grid[point.1 as usize][point.0 as usize] += 1;
    }

    for row in &grid {
        println!("{}", join_vec(" ", row));
    }

    let result: i32 = grid
        .iter()
        .flatten()
        .map(|v| if *v > 1 { 1 } else { 0 })
        .sum();

    println!("Part 1 result is {}", result)
}

fn part2() {
    let file_contents = fs::read_to_string("input.txt").expect("No input found");
    let lines: Vec<Line> = file_contents
        .lines()
        .map(|l| Line::from_str(l))
        // .filter(|l| l.is_horizontal() || l.is_vertical())
        .collect();

    for line in &lines {
        println!("Line is {}", line);
        let line_points: Vec<Point> = line.interpolate_line();
        println!("Full line: {}", join_points(&line_points));
    }

    let all_points = lines
        .iter()
        .map(|line| line.interpolate_line())
        .flatten()
        .collect();
    let grid_max = max_point(&all_points);
    let mut grid: Vec<Vec<i32>> = (0..(grid_max.1 + 1))
        .map(|_| (0..(grid_max.0 + 1)).map(|_| 0).collect::<Vec<i32>>())
        .collect();

    for point in &all_points {
        grid[point.1 as usize][point.0 as usize] += 1;
    }

    for row in &grid {
        println!("{}", join_vec(" ", row));
    }

    let result: i32 = grid
        .iter()
        .flatten()
        .map(|v| if *v > 1 { 1 } else { 0 })
        .sum();

    println!("Part 1 result is {}", result)
}

fn main() {
    part1();
    part2();
}