day_08.rs

use common::{solution, Answer};

solution!("Treetop Tree House", 8);

fn part_a(input: &str) -> Answer {
    let trees = parse_trees(input);
    let mut count = 0;

    for row in 0..trees.len() {
        for col in 0..trees[row].len() {
            let height = trees[row][col];
            if trees[..row].iter().all(|x| x[col] < height)
                || trees[row][..col].iter().all(|x| x < &height)
                || trees[row + 1..].iter().all(|x| x[col] < height)
                || trees[row][col + 1..].iter().all(|x| x < &height)
            {
                count += 1;
            }
        }
    }

    count.into()
}

fn part_b(input: &str) -> Answer {
    let trees = parse_trees(input);
    let mut count = 0;

    for row in 0..trees.len() {
        for col in 0..trees[row].len() {
            let mut ctx = (1, trees[row][col]);
            process_slice(&mut ctx, trees[..row].iter().map(|x| x[col]).rev());
            process_slice(&mut ctx, trees[row][..col].iter().rev().copied());
            process_slice(&mut ctx, trees[row + 1..].iter().map(|x| x[col]));
            process_slice(&mut ctx, trees[row][col + 1..].iter().copied());
            count = count.max(ctx.0);
        }
    }

    count.into()
}

fn parse_trees(inp: &str) -> Vec<Vec<usize>> {
    inp.lines()
        .map(|i| {
            i.chars()
                .filter(|x| x.is_ascii_digit())
                .filter_map(|x| x.to_digit(10))
                .map(|x| x as usize)
                .collect()
        })
        .collect()
}

fn process_slice((local_best, height): &mut (usize, usize), iter: impl Iterator<Item = usize>) {
    let mut score = 0;

    for i in iter {
        score += 1;
        if i >= *height {
            break;
        }
    }

    *local_best *= score;
}