aoc2024/src/day08.rs

#![allow(clippy::cast_sign_loss, clippy::cast_possible_wrap)]
use std::collections::HashSet;
use tracing::{debug, trace};

pub fn pt1(input: &str) -> usize {
    let char_positions = input
        .lines()
        .map(str::chars)
        .enumerate()
        .flat_map(|(y, line)| line.enumerate().map(move |(x, char)| (char, x, y)))
        .collect::<Vec<_>>();
    let dims = (input.lines().next().unwrap().len(), input.lines().count());
    debug!("dims: {dims:?}");
    let node_positions = char_positions
        .iter()
        .filter(|(c, _, _)| *c != '.')
        .collect::<Vec<_>>();
    let unique_nodes = node_positions
        .iter()
        .map(|(c, _, _)| *c)
        .collect::<HashSet<_>>();
    let mut antinode_positions = HashSet::<(usize, usize)>::new();
    for node in unique_nodes {
        let matching_node_positions = node_positions
            .iter()
            .filter(|(c, _, _)| *c == node)
            .collect::<Vec<_>>()
            .into_iter();
        for (_, node_x, node_y) in matching_node_positions.clone() {
            for (_, other_node_x, other_node_y) in matching_node_positions.clone() {
                trace!(
                    "comparing ({node_x}, {node_y}) with ({other_node_x}, {other_node_y}): {:?}, {:?}",
                    node_x.cmp(other_node_x), node_y.cmp(other_node_y)
                );
                if node_x == other_node_x && node_y == other_node_y {
                    continue;
                }
                let dx = *node_x as isize - *other_node_x as isize;
                let dy = *node_y as isize - *other_node_y as isize;
                let prev_x = *node_x as isize + dx;
                let prev_y = *node_y as isize + dy;
                let post_x = *other_node_x as isize - dx;
                let post_y = *other_node_y as isize - dy;
                if prev_x >= 0
                    && (prev_x as usize) < dims.0
                    && prev_y >= 0
                    && (prev_y as usize) < dims.1
                {
                    antinode_positions.insert((prev_x as usize, prev_y as usize));
                }
                if post_x >= 0
                    && (post_x as usize) < dims.0
                    && post_y >= 0
                    && (post_y as usize) < dims.1
                {
                    antinode_positions.insert((post_x as usize, post_y as usize));
                }
            }
        }
        debug!("antinodes for {node}: {antinode_positions:?}");
    }
    let new_map = input
        .lines()
        .enumerate()
        .map(|(y, line)| {
            line.chars()
                .enumerate()
                .map(|(x, c)| {
                    if c != '.' || !antinode_positions.contains(&(x, y)) {
                        c
                    } else {
                        '#'
                    }
                })
                .collect::<String>()
        })
        .collect::<Vec<_>>()
        .join("\n");
    debug!("new Map: \n{new_map}");
    antinode_positions.len()
}
// 225 is too high
pub fn pt2(input: &str) -> usize {
    let char_positions = input
        .lines()
        .map(str::chars)
        .enumerate()
        .flat_map(|(y, line)| line.enumerate().map(move |(x, char)| (char, x, y)))
        .collect::<Vec<_>>();
    let dims = (input.lines().next().unwrap().len(), input.lines().count());
    debug!("dims: {dims:?}");
    let node_positions = char_positions
        .iter()
        .filter(|(c, _, _)| *c != '.')
        .collect::<Vec<_>>();
    let unique_nodes = node_positions
        .iter()
        .map(|(c, _, _)| *c)
        .collect::<HashSet<_>>();
    let mut antinode_positions = HashSet::<(usize, usize)>::new();
    for node in unique_nodes {
        let matching_node_positions = node_positions
            .iter()
            .filter(|(c, _, _)| *c == node)
            .collect::<Vec<_>>()
            .into_iter();
        for (_, node_x, node_y) in matching_node_positions.clone() {
            for (_, other_node_x, other_node_y) in matching_node_positions.clone() {
                trace!(
                "comparing ({node_x}, {node_y}) with ({other_node_x}, {other_node_y}): {:?}, {:?}",
                node_x.cmp(other_node_x), node_y.cmp(other_node_y)
            );
                if node_x == other_node_x && node_y == other_node_y {
                    continue;
                }
                let dx = *node_x as isize - *other_node_x as isize;
                let dy = *node_y as isize - *other_node_y as isize;
                let mut prev_x = *node_x as isize;
                let mut prev_y = *node_y as isize;
                while prev_x >= 0
                    && (prev_x as usize) < dims.0
                    && prev_y >= 0
                    && (prev_y as usize) < dims.1
                {
                    antinode_positions.insert((prev_x as usize, prev_y as usize));
                    prev_x += dx;
                    prev_y += dy;
                }
                let mut post_x = *other_node_x as isize;
                let mut post_y = *other_node_y as isize;
                while post_x >= 0
                    && (post_x as usize) < dims.0
                    && post_y >= 0
                    && (post_y as usize) < dims.1
                {
                    antinode_positions.insert((post_x as usize, post_y as usize));
                    post_x -= dx;
                    post_y -= dy;
                }
            }
        }
        debug!("antinodes for {node}: {antinode_positions:?}");
    }
    let new_map = input
        .lines()
        .enumerate()
        .map(|(y, line)| {
            line.chars()
                .enumerate()
                .map(|(x, c)| {
                    if c != '.' || !antinode_positions.contains(&(x, y)) {
                        c
                    } else {
                        '#'
                    }
                })
                .collect::<String>()
        })
        .collect::<Vec<_>>()
        .join("\n");
    debug!("new Map: \n{new_map}");
    antinode_positions.len()
}

#[cfg(test)]
mod tests {
    use tracing_test::traced_test;

    use super::{pt1, pt2};
    use std::fs::read_to_string;

    #[traced_test]
    #[test]
    pub fn test_pt1() {
        let input =
            read_to_string("./inputs/day08/example.txt").expect("Missing example.txt for day08");
        assert_eq!(pt1(&input), 14)
    }

    #[traced_test]
    #[test]
    pub fn test_pt2() {
        let input =
            read_to_string("./inputs/day08/example.txt").expect("Missing example.txt for day08");

        assert_eq!(pt2(&input), 34)
    }
}