AoC2021/src/day05.rs

use std::cmp::Ordering;
use std::collections::HashMap;
use crate::Day;
use anyhow::Result;

pub struct Day05(Vec<Path>);

#[derive(Clone, Eq, PartialEq, Ord, PartialOrd, Debug)]
struct Path {
    start: Coordinate,
    end: Coordinate,
    covers: Vec<Coordinate>,
}

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

impl Day for Day05 {
    fn init(content: String) -> Result<Self> {
        let paths = content.lines().map(str_to_vent).collect::<Result<Vec<Path>, _>>()?;
        Ok(Self(paths))
    }

    fn part1(&self) -> Result<String> {
        let new_vents = self.0.iter().filter(|p| p.is_straight()).cloned().collect::<Vec<Path>>();
        Ok(format!("{}", covered_twice(&new_vents)))
    }

    fn part2(&self) -> Result<String> {
        Ok(format!("{}", covered_twice(&self.0)))
    }
}

fn covered_twice(vents: &[Path]) -> usize {
    let mut m = HashMap::new();
    for vent in vents {
        for cover in &vent.covers {
            let m = m.entry(cover).or_insert(0);
            *m += 1;
        }
    }

    m.values().copied().filter(|x| *x >= 2).count()
}

impl Path {
    fn is_straight(&self) -> bool {
        self.start.x == self.end.x || self.start.y == self.end.y
    }
}

impl Coordinate {
    fn dir_to(&self, other: &Coordinate) -> Direction {
        return if self.x < other.x {
            match self.y.cmp(&other.y) {
                Ordering::Less => Direction::SE,
                Ordering::Equal => Direction::E,
                Ordering::Greater => Direction::NE,
            }
        } else if self.x == other.x {
            match self.y.cmp(&other.y) {
                Ordering::Less => Direction::S,
                Ordering::Equal => panic!("why are the start and end equal??"),
                Ordering::Greater => Direction::N,
            }
        } else if self.y < other.y {
            Direction::SW
        } else if self.y == other.y {
            Direction::W
        } else {
            Direction::NW
        };
    }

    #[cfg(test)]
    fn new(x: i64, y: i64) -> Self {
        Coordinate { x, y }
    }

    fn from_vec(v: &[i64]) -> Self {
        Coordinate { x: v[0], y: v[1] }
    }
}

#[derive(Eq, PartialEq, Debug)]
enum Direction {
    NE,
    NW,
    SE,
    SW,
    N,
    E,
    W,
    S,
}

impl Direction {
    fn coord_diff(&self) -> (i64, i64) {
        match self {
            Direction::NE => (1, -1),
            Direction::NW => (-1, -1),
            Direction::SE => (1, 1),
            Direction::SW => (-1, 1),
            Direction::N => (0, -1),
            Direction::E => (1, 0),
            Direction::W => (-1, 0),
            Direction::S => (0, 1),
        }
    }
}

fn str_to_vent(st: &str) -> Result<Path> {
    let mut v = st.split(" -> ");
    let a = v.next().ok_or_else(|| anyhow::Error::msg("could not get next..."))?;
    let b = v.next().ok_or_else(|| anyhow::Error::msg("could not get next..."))?;
    let start = a.split(',').map(str::parse).collect::<Result<Vec<i64>,_>>()?;
    let end = b.split(',').map(str::parse).collect::<Result<Vec<i64>,_>>()?;
    let start = Coordinate::from_vec(&start);
    let end = Coordinate::from_vec(&end);

    let dir = start.dir_to(&end).coord_diff();
    let mut covers = vec![];
    let mut c = start.clone();

    while c != end {
        covers.push(c.clone());
        c.x += dir.0;
        c.y += dir.1;
    }
    covers.push(end.clone());

    Ok(Path {
        start,
        end,
        covers,
    })
}

#[cfg(test)]
mod tests {
    use crate::{Day05, day_tests};
    use crate::day05::{Coordinate, Direction};
    use crate::day::Day;
    use anyhow::Result;

    const INPUT: &str = r"0,9 -> 5,9
8,0 -> 0,8
9,4 -> 3,4
2,2 -> 2,1
7,0 -> 7,4
6,4 -> 2,0
0,9 -> 2,9
3,4 -> 1,4
0,0 -> 8,8
5,5 -> 8,2";

    #[test]
    fn directions() {
        assert_eq!(Coordinate::new(5, 5).dir_to(&Coordinate::new(0, 0)), Direction::NW);
        assert_eq!(Coordinate::new(5, 5).dir_to(&Coordinate::new(9, 9)), Direction::SE);
        assert_eq!(Coordinate::new(5, 5).dir_to(&Coordinate::new(9, 0)), Direction::NE);
        assert_eq!(Coordinate::new(5, 5).dir_to(&Coordinate::new(0, 9)), Direction::SW);
        assert_eq!(Coordinate::new(5, 5).dir_to(&Coordinate::new(0, 5)), Direction::W);
        assert_eq!(Coordinate::new(5, 5).dir_to(&Coordinate::new(5, 0)), Direction::N);
        assert_eq!(Coordinate::new(5, 5).dir_to(&Coordinate::new(9, 5)), Direction::E);
        assert_eq!(Coordinate::new(5, 5).dir_to(&Coordinate::new(5, 9)), Direction::S);
    }

    #[test]
    fn part1_test() -> Result<()> {
        let d = Day05::init(INPUT.to_string())?;
        assert_eq!("5", d.part1()?);
        Ok(())
    }

    #[test]
    fn part2_test() -> Result<()> {
        let d = Day05::init(INPUT.to_string())?;
        assert_eq!("12", d.part2()?);
        Ok(())
    }

    day_tests!(Day05, "05", "6564", "19172");
}