aoc-2021/src/t05_hydrothermal_venture/mod.rs

use std::{
    cmp::Ordering,
    collections::{HashMap, HashSet},
    fmt::Display,
    io::{BufRead, BufReader},
};

use crate::types::TestMode;

#[derive(Clone, Debug, PartialEq, Eq, Hash)]
struct Point {
    x: i64,
    y: i64,
}

impl Display for Point {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.write_fmt(format_args!("({}, {})", self.x, self.y))
            .unwrap();
        Ok(())
    }
}

#[derive(Debug, PartialEq, Eq, Hash)]
struct Line {
    p1: Point,
    p2: Point,
}

impl Display for Line {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.write_fmt(format_args!("[{} -> {}]", self.p1, self.p2))
            .unwrap();
        Ok(())
    }
}

impl Line {
    fn points(&self) -> HashSet<Point> {
        let mut res = HashSet::new();

        let dx = Self::sign(self.p2.x - self.p1.x);
        let dy = Self::sign(self.p2.y - self.p1.y);

        let mut x = self.p1.x;
        let mut y = self.p1.y;
        loop {
            let p = Point { x, y };

            res.insert(p);

            if x == self.p2.x && y == self.p2.y {
                break;
            }

            x += dx;
            y += dy;
        }

        res
    }

    fn sign(expr: i64) -> i64 {
        match expr.cmp(&0) {
            Ordering::Less => -1,
            Ordering::Equal => 0,
            Ordering::Greater => 1,
        }
    }
}

struct Input {
    lines: Vec<Line>,
}

fn parse_input(test_mode: TestMode) -> Input {
    let f = test_mode.input_file(file!());
    let br = BufReader::new(f);
    let lines = br
        .lines()
        .map(|line| {
            let line = line.unwrap();
            let mut s = line.split_terminator(" -> ");

            let mut m = s.next().unwrap().split_terminator(',');
            let p1 = Point {
                x: m.next().unwrap().parse().unwrap(),
                y: m.next().unwrap().parse().unwrap(),
            };

            let mut m = s.next().unwrap().split_terminator(',');
            let p2 = Point {
                x: m.next().unwrap().parse().unwrap(),
                y: m.next().unwrap().parse().unwrap(),
            };

            Line { p1, p2 }
        })
        .collect();

    Input { lines }
}

pub fn hydrothermal_venture_1(test_mode: TestMode) {
    let input = parse_input(test_mode);

    let orthogonal_lines: Vec<_> = input
        .lines
        .into_iter()
        .filter(|line| line.p1.x == line.p2.x || line.p1.y == line.p2.y)
        .collect();

    let mut point_count = HashMap::<Point, i64>::new();
    for line in orthogonal_lines {
        for point in line.points() {
            *point_count.entry(point).or_insert(0) += 1;
        }
    }
    let num_intersections = point_count
        .iter()
        .filter(|point_usages| point_usages.1 > &1)
        .count();

    println!("{}", num_intersections);
}

pub fn hydrothermal_venture_2(test_mode: TestMode) {
    let lines = parse_input(test_mode).lines;

    let mut point_count = HashMap::<Point, i64>::new();

    for line in lines {
        for point in line.points() {
            *point_count.entry(point).or_insert(0) += 1;
        }
    }
    let num_intersections = point_count
        .iter()
        .filter(|point_usages| point_usages.1 > &1)
        .count();

    println!("{}", num_intersections);
}