Advent of Code 2023 - DAY 11

Problem Day 11: Cosmic Expansion

Here the day 11 problem statement: https://adventofcode.com/2023/day/11

Solution Part 1

pub fn build_galaxies(input: &str) -> Vec<(usize, usize)> {
    let mut galaxies: Vec<(usize, usize)> = Vec::new();

    for (i, row) in input.lines().enumerate() {
        for (j, col) in row.chars().enumerate() {
            if col.eq(&'#') {
                galaxies.push((i, j))
            }
        }
    }
    galaxies
}

pub fn extract_empty_rows(galaxies: &mut Vec<(usize, usize)>) -> Vec<usize> {
    let mut empty_rows: Vec<usize> = Vec::new();

    galaxies.sort_by(|a, b| a.0.cmp(&b.0));

    for i in 0..galaxies.len() - 1 {
        if galaxies[i + 1].0 - galaxies[i].0 > 1 {
            for j in galaxies[i].0 + 1..galaxies[i + 1].0 {
                empty_rows.push(j);
            }
        }
    }

    empty_rows
}

pub fn extract_empty_cols(galaxies: &mut Vec<(usize, usize)>) -> Vec<usize> {
    let mut empty_cols: Vec<usize> = Vec::new();

    galaxies.sort_by(|a, b| a.1.cmp(&b.1));

    for i in 0..galaxies.len() - 1 {
        if galaxies[i + 1].1 - galaxies[i].1 > 1 {
            for j in galaxies[i].1 + 1..galaxies[i + 1].1 {
                empty_cols.push(j);
            }
        }
    }

    empty_cols
}

pub fn expand_galaxies(
    galaxies: &mut [(usize, usize)],
    empty_rows: &[usize],
    empty_cols: &[usize],
    rate: usize,
) {
    for galaxy in galaxies {
        let num_step_x = empty_rows.iter().filter(|r| **r < galaxy.0).count() as usize;
        let num_step_y = empty_cols.iter().filter(|c| **c < galaxy.1).count() as usize;

        galaxy.0 += (num_step_x * (rate - 1)) as usize;
        galaxy.1 += (num_step_y * (rate - 1)) as usize;
    }
}

pub fn solve(input: &str, rate: usize) -> usize {
    let mut galaxies: Vec<(usize, usize)> = build_galaxies(input);
    let empty_rows: Vec<usize> = extract_empty_rows(&mut galaxies);
    let empty_cols: Vec<usize> = extract_empty_cols(&mut galaxies);

    expand_galaxies(&mut galaxies, &empty_rows, &empty_cols, rate);

    let mut distances_sum: usize = 0;
    for i in 0..galaxies.len() {
        for j in i + 1..galaxies.len() {
            let distance = (galaxies[i].0 as i32 - galaxies[j].0 as i32).abs()
                + (galaxies[i].1 as i32 - galaxies[j].1 as i32).abs();

            distances_sum += distance as usize;
        }
    }

    distances_sum
}

pub fn part1(input: &str) -> usize {
    solve(input, 2)
}

Solution Part 2

pub fn part2(input: &str) -> usize {
    solve(input, 1_000_000)
}

Here the repository with all puzzle solutions.