advent-2022-rust/src/days/day08/mod.rs

use super::template::{DayTrait, ResultType};
use itertools::{iproduct, FoldWhile, Itertools};
use thiserror::Error;

const DAY_NUMBER: usize = 8;

pub struct Day;

impl DayTrait for Day {
    fn get_day_number(&self) -> usize {
        DAY_NUMBER
    }

    fn part1(&self, lines: &[String]) -> anyhow::Result<ResultType> {
        let forest = Forest::parse(lines)?;
        let result = forest.count_visible();
        Ok(ResultType::Integer(result))
    }

    fn part2(&self, lines: &[String]) -> anyhow::Result<ResultType> {
        let forest = Forest::parse(lines)?;
        let result = forest.best_score();
        Ok(ResultType::Integer(result))
    }
}

#[derive(Debug, Error)]
enum ForestError {
    #[error("Not a legal digit: {0}")]
    NoLegalDigit(char),

    #[error("The Forst is not a rectangle")]
    NonRectangleForest,

    #[error("Zero Sized Forest not allowed")]
    NoZeroSizedForest,
}

#[derive(Debug)]
struct Forest {
    trees: Vec<Vec<u32>>,
    width: usize,
    height: usize,
}

impl Forest {
    pub fn create(trees: Vec<Vec<u32>>) -> Result<Self, ForestError> {
        let height = trees.len();
        if height == 0 {
            return Err(ForestError::NoZeroSizedForest);
        }
        let width = trees[0].len();
        if width == 0 {
            return Err(ForestError::NoZeroSizedForest);
        }

        for row in trees.iter() {
            if row.len() != width {
                return Err(ForestError::NonRectangleForest);
            }
        }

        Ok(Forest {
            trees,
            width,
            height,
        })
    }

    pub fn parse(lines: &[String]) -> Result<Forest, ForestError> {
        lines
            .iter()
            .map(|line| {
                line.chars()
                    .map(|height| height.to_digit(10).ok_or(ForestError::NoLegalDigit(height)))
                    .collect::<Result<Vec<_>, _>>()
            })
            .collect::<Result<Vec<_>, _>>()
            .and_then(Forest::create)
    }

    pub fn count_visible(&self) -> i64 {
        let mut vis_count = 2 * (self.width + self.height - 2) as i64;
        let mut visible = vec![vec![false; self.width - 2]; self.height - 2];

        for y in 1..self.height - 1 {
            let mut talest_seen = self.trees[y][0];
            for x in 1..self.width - 1 {
                let tree = self.trees[y][x];
                if tree > talest_seen {
                    vis_count += 1;
                    visible[y - 1][x - 1] = true;
                    talest_seen = self.trees[y][x];
                }
            }

            let mut talest_seen = self.trees[y][self.width - 1];
            for x in (1..self.width - 1).rev() {
                let tree = self.trees[y][x];
                if tree > talest_seen {
                    if !visible[y - 1][x - 1] {
                        vis_count += 1;
                        visible[y - 1][x - 1] = true;
                    }
                    talest_seen = self.trees[y][x];
                }
            }
        }

        for x in 1..self.width - 1 {
            let mut talest_seen = self.trees[0][x];
            for y in 1..self.height - 1 {
                let tree = self.trees[y][x];
                if tree > talest_seen {
                    if !visible[y - 1][x - 1] {
                        vis_count += 1;
                        visible[y - 1][x - 1] = true;
                    }
                    talest_seen = self.trees[y][x];
                }
            }

            let mut talest_seen = self.trees[self.height - 1][x];
            for y in (1..self.height - 1).rev() {
                let tree = self.trees[y][x];
                if tree > talest_seen {
                    if !visible[y - 1][x - 1] {
                        vis_count += 1;
                        visible[y - 1][x - 1] = true;
                    }
                    talest_seen = self.trees[y][x];
                }
            }
        }

        vis_count
    }

    pub fn best_score(&self) -> i64 {
        iproduct!(1..self.width - 1, 1..self.height - 1)
            .map(|(x, y)| self.score(x, y))
            .max()
            // None can only happen when we have a forrest with no inner trees.
            // In that case 0 is the correct solution.
            // We already forbid zero height and zero width forests during create.
            .unwrap_or(0)
    }

    fn score(&self, x: usize, y: usize) -> i64 {
        let tree = self.trees[y][x];
        let left = (0..x)
            .rev()
            .fold_while(0, |acc, x| {
                if self.trees[y][x] < tree {
                    FoldWhile::Continue(acc + 1)
                } else {
                    FoldWhile::Done(acc + 1)
                }
            })
            .into_inner();
        let right = (x + 1..self.width)
            .fold_while(0, |acc, x| {
                if self.trees[y][x] < tree {
                    FoldWhile::Continue(acc + 1)
                } else {
                    FoldWhile::Done(acc + 1)
                }
            })
            .into_inner();
        let up = (0..y)
            .rev()
            .fold_while(0, |acc, y| {
                if self.trees[y][x] < tree {
                    FoldWhile::Continue(acc + 1)
                } else {
                    FoldWhile::Done(acc + 1)
                }
            })
            .into_inner();
        let down = (y + 1..self.height)
            .fold_while(0, |acc, y| {
                if self.trees[y][x] < tree {
                    FoldWhile::Continue(acc + 1)
                } else {
                    FoldWhile::Done(acc + 1)
                }
            })
            .into_inner();

        left * right * up * down
    }
}

#[cfg(test)]
mod test {
    use super::*;
    use crate::common::file::read_lines;
    use anyhow::Result;

    #[test]
    fn test_parse() -> Result<()> {
        let day = Day {};
        let lines = read_lines(day.get_day_number(), "example01.txt")?;
        let forest = Forest::parse(&lines)?;
        assert_eq!(forest.width, 5);
        assert_eq!(forest.height, 5);

        Ok(())
    }

    #[test]
    fn test_part1() -> Result<()> {
        let day = Day {};
        let lines = read_lines(day.get_day_number(), "example01.txt")?;
        let expected = ResultType::Integer(21);
        let result = day.part1(&lines)?;
        assert_eq!(result, expected);

        Ok(())
    }

    #[test]
    fn test_part2() -> Result<()> {
        let day = Day {};
        let lines = read_lines(day.get_day_number(), "example01.txt")?;
        let expected = ResultType::Integer(8);
        let result = day.part2(&lines)?;
        assert_eq!(result, expected);

        Ok(())
    }
}