advent-of-code/2023/src/day3.rs

use std::collections::HashSet;

const INPUT: &str = include_str!("../data/day3.txt");

pub fn day3a() -> String {
    format!("{}", sum_parts(INPUT.to_owned()))
}

pub fn day3b() -> String {
    format!(
        "{}",
        find_gears(INPUT.to_owned())
            .into_iter()
            .map(|gear| gear.ratio())
            .fold(0, |acc, val| acc + val)
    )
}

#[derive(Clone, Debug, PartialEq)]
struct Addr {
    row: usize,
    start: usize,
    end: usize,
}

impl Addr {
    fn span(&self) -> Vec<(usize, usize)> {
        (self.start..self.end + 1)
            .map(|addr| (self.row, addr))
            .collect()
    }
}

#[derive(Clone, Debug, PartialEq)]
struct Gear(u32, u32);

impl Gear {
    fn ratio(&self) -> u32 {
        self.0 * self.1
    }
}

fn sum_parts(schematic: String) -> u32 {
    parts(schematic).into_iter().fold(0, |acc, val| acc + val.0)
}

fn parts(schematic: String) -> Vec<(u32, Addr)> {
    let sc = schematic
        .lines()
        .map(|l| l.to_owned())
        .collect::<Vec<String>>();
    let numbers = find_numbers(schematic.clone());
    numbers
        .into_iter()
        .filter(|number| is_part(&sc, number))
        .collect::<Vec<(u32, Addr)>>()
}

fn find_gears(schematic: String) -> Vec<Gear> {
    let sc = schematic
        .lines()
        .map(|l| l.to_owned())
        .collect::<Vec<String>>();
    let max_row = sc.len();
    let max_col = sc[0].len();
    let parts = parts(schematic);
    let splats = find_splats(sc)
        .into_iter()
        .map(|(row, col)| {
            halo(
                Addr {
                    row,
                    start: col,
                    end: col,
                },
                max_row - 1,
                max_col - 1,
            )
        })
        .collect::<Vec<Vec<(usize, usize)>>>();

    let mut gears = vec![];
    for splat in splats {
        let overlap = parts
            .iter()
            .filter(|part| part_within_halo(splat.clone(), part.1.clone()))
            .map(|part| part.0)
            .collect::<Vec<u32>>();
        if overlap.len() == 2 {
            gears.push(Gear(overlap[0], overlap[1]));
        }
    }

    gears
}

fn part_within_halo(halo1: Vec<(usize, usize)>, part: Addr) -> bool {
    let halo1: HashSet<(usize, usize)> = halo1.into_iter().collect::<HashSet<(usize, usize)>>();
    let halo2: HashSet<(usize, usize)> =
        part.span().into_iter().collect::<HashSet<(usize, usize)>>();

    halo1.intersection(&halo2).count() > 0
}

fn is_part(schematic: &Vec<String>, number: &(u32, Addr)) -> bool {
    halo(
        number.1.clone(),
        schematic.len() - 1,
        schematic[0].len() - 1,
    )
    .into_iter()
    .any(|(row, col)| {
        let cell = schematic[row].chars().nth(col).unwrap();
        !cell.is_digit(10) && cell != '.'
    })
}

fn halo(addr: Addr, max_row: usize, max_col: usize) -> Vec<(usize, usize)> {
    let mut halo: Vec<(i32, i32)> = vec![];

    for r in addr.start..addr.end + 1 {
        halo.push((addr.row as i32 - 1, r as i32));
        halo.push((addr.row as i32 + 1, r as i32));
    }

    halo.push((addr.row as i32 - 1, addr.start as i32 - 1));
    halo.push((addr.row as i32, addr.start as i32 - 1));
    halo.push((addr.row as i32 + 1, addr.start as i32 - 1));
    halo.push((addr.row as i32 - 1, addr.end as i32 + 1));
    halo.push((addr.row as i32, addr.end as i32 + 1));
    halo.push((addr.row as i32 + 1, addr.end as i32 + 1));

    halo.into_iter()
        .filter(|(row, col)| {
            *row >= 0 && *row <= max_row as i32 && *col >= 0 && *col <= max_col as i32
        })
        .map(|(row, col)| (row as usize, col as usize))
        .collect()
}

fn find_numbers(schematic: String) -> Vec<(u32, Addr)> {
    let mut result = vec![];
    for (idx, line) in schematic.lines().enumerate() {
        let mut numbers = find_numbers_in_line(line)
            .into_iter()
            .map(|(number, start, len)| {
                (
                    number,
                    Addr {
                        row: idx,
                        start,
                        end: start + len - 1,
                    },
                )
            })
            .collect::<Vec<(u32, Addr)>>();
        result.append(&mut numbers);
    }
    result
}

fn find_numbers_in_line(line: &str) -> Vec<(u32, usize, usize)> {
    let mut numbers = vec![];

    let mut start_idx: usize = 0;
    let mut number: Option<String> = None;

    for idx in 0..line.len() {
        match (number.take(), line.chars().nth(idx).unwrap()) {
            (None, c) if c.is_digit(10) => {
                start_idx = idx;
                number = Some(String::from(c));
            }
            (Some(mut num), c) if c.is_digit(10) => {
                num.push(c);
                number = Some(num);
            }
            (Some(num), _) => {
                numbers.push((num, start_idx));
                number = None;
            }
            (_, _) => {}
        }
    }

    if let Some(num) = number {
        numbers.push((num, start_idx));
    }

    numbers
        .into_iter()
        .map(|(number, start_idx)| (number.parse::<u32>().unwrap(), start_idx, number.len()))
        .collect()
}

fn find_splats(schematic: Vec<String>) -> Vec<(usize, usize)> {
    schematic
        .into_iter()
        .enumerate()
        .map(|(row_idx, row)| {
            row.chars()
                .enumerate()
                .filter_map(|(col_idx, c)| {
                    if is_splat(c) {
                        Some((row_idx, col_idx))
                    } else {
                        None
                    }
                })
                .collect::<Vec<(usize, usize)>>()
        })
        .flatten()
        .collect::<Vec<(usize, usize)>>()
}

fn is_symbol(c: char) -> bool {
    !c.is_digit(10) && c != '.'
}

fn is_splat(c: char) -> bool {
    c == '*'
}

#[cfg(test)]
mod test {
    use super::*;

    const INPUT: &str = "467..114..
...*......
..35..633.
......#...
617*......
.....+.58.
..592.....
......755.
...$.*....
.664.598..";

    #[test]
    fn part_1() {
        assert_eq!(
            parts(INPUT.to_owned())
                .into_iter()
                .map(|part| part.0)
                .collect::<Vec<u32>>(),
            vec![467, 35, 633, 617, 592, 755, 664, 598]
        );

        assert_eq!(sum_parts(INPUT.to_owned()), 4361);
    }

    #[test]
    fn test_find_numbers() {
        println!("{:?}", find_numbers(INPUT.to_owned()));
        assert_eq!(
            find_numbers(INPUT.to_owned()),
            vec![
                (
                    467,
                    Addr {
                        row: 0,
                        start: 0,
                        end: 2
                    }
                ),
                (
                    114,
                    Addr {
                        row: 0,
                        start: 5,
                        end: 7
                    }
                ),
                (
                    35,
                    Addr {
                        row: 2,
                        start: 2,
                        end: 3
                    }
                ),
                (
                    633,
                    Addr {
                        row: 2,
                        start: 6,
                        end: 8
                    }
                ),
                (
                    617,
                    Addr {
                        row: 4,
                        start: 0,
                        end: 2
                    }
                ),
                (
                    58,
                    Addr {
                        row: 5,
                        start: 7,
                        end: 8,
                    }
                ),
                (
                    592,
                    Addr {
                        row: 6,
                        start: 2,
                        end: 4,
                    }
                ),
                (
                    755,
                    Addr {
                        row: 7,
                        start: 6,
                        end: 8,
                    }
                ),
                (
                    664,
                    Addr {
                        row: 9,
                        start: 1,
                        end: 3,
                    }
                ),
                (
                    598,
                    Addr {
                        row: 9,
                        start: 5,
                        end: 7,
                    }
                )
            ]
        );
    }

    #[test]
    fn test_find_numbers_in_line() {
        let test_cases = vec![
            ("...*......", vec![]),
            (".664.598..", vec![(664, 1, 3), (598, 5, 3)]),
            ("..35..633.", vec![(35, 2, 2), (633, 6, 3)]),
            (
                "......883.....*163...782",
                vec![(883, 6, 3), (163, 15, 3), (782, 21, 3)],
            ),
        ];
        for (input, expected) in test_cases {
            assert_eq!(find_numbers_in_line(input), expected);
        }
    }

    #[test]
    fn test_halo() {
        let schematic = INPUT.lines().map(|l| l.to_owned()).collect::<Vec<String>>();
        let number = Addr {
            row: 0,
            start: 0,
            end: 2,
        };
        assert_eq!(
            halo(number, schematic.len() - 1, schematic[0].len() - 1),
            vec![(1, 0), (1, 1), (1, 2), (0, 3), (1, 3)]
        );

        assert_eq!(
            halo(
                Addr {
                    row: 1,
                    start: 1,
                    end: 1
                },
                schematic.len() - 1,
                schematic[0].len() - 1
            ),
            vec![
                (0, 1),
                (2, 1),
                (0, 0),
                (1, 0),
                (2, 0),
                (0, 2),
                (1, 2),
                (2, 2)
            ]
        );
        assert_eq!(
            halo(
                Addr {
                    row: 6,
                    start: 2,
                    end: 4,
                },
                schematic.len() - 1,
                schematic[0].len() - 1
            ),
            vec![
                (5, 2),
                (7, 2),
                (5, 3),
                (7, 3),
                (5, 4),
                (7, 4),
                (5, 1),
                (6, 1),
                (7, 1),
                (5, 5),
                (6, 5),
                (7, 5),
            ]
        );
    }

    #[test]
    fn test_find_gears() {
        let gears = find_gears(INPUT.to_owned());
        assert_eq!(gears, vec![Gear(467, 35), Gear(755, 598)]);
        assert_eq!(
            gears.into_iter().map(|g| g.ratio()).collect::<Vec<u32>>(),
            vec![16345, 451490]
        );
    }
}