this post was submitted on 05 Dec 2023
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Advent Of Code

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Day 5: If You Give a Seed a Fertilizer


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[–] abclop99@beehaw.org 1 points 11 months ago

[Rust]

Part 2

use std::fs;
use std::path::PathBuf;

use clap::Parser;

#[derive(Parser)]
#[command(author, version, about, long_about = None)]
struct Cli {
    input_file: PathBuf,
}

/// Start < end
#[derive(Debug, Copy, Clone)]
struct Range {
    start: Idx,
    end: Idx,
}

impl From> for Range {
    fn from(item: std::ops::Range) -> Self {
        Range {
            start: item.start,
            end: item.end,
        }
    }
}

impl std::ops::Add for Range {
    type Output = Self;

    fn add(self, offset: i64) -> Self {
        Range {
            start: self.start + offset,
            end: self.end + offset,
        }
    }
}

#[derive(Debug, Copy, Clone)]
enum Value {
    Unmapped(Range),
    Mapped(Range),
}

impl Value {
    fn value(self) -> Range {
        match self {
            Self::Mapped(n) => n,
            Self::Unmapped(n) => n,
        }
    }

    fn min(self) -> i64 {
        self.value().start
    }
}

fn main() {
    // Parse CLI arguments
    let cli = Cli::parse();

    // Read file
    let input_text = fs::read_to_string(&cli.input_file)
        .expect(format!("File \"{}\" not found", cli.input_file.display()).as_str());

    println!("{}", input_text);

    // Split into seeds and individual maps
    let mut maps_text = input_text.split("\n\n");
    let seeds_text = maps_text.next().expect("Seeds");

    // Seed numbers; will be mapped to the final locations
    let seed_numbers: Vec = parse_seeds(seeds_text);
    let seed_numbers = parse_seed_ranges(seed_numbers);
    let mut seed_values: Vec = seed_numbers.iter().map(|n| Value::Unmapped(*n)).collect();

    eprintln!("Seeds: {:?}", seed_values);

    // Apply maps to seeds
    for map_text in maps_text {
        let mut map_ranges_text = map_text.lines();
        let map_description = map_ranges_text
            .next()
            .expect("There should be a description of the map here");
        eprintln!("Map: {}", map_description);

        // Apply ranges to seeds
        // Map structure:
        // dest start, source start, range length
        for range_text in map_ranges_text {
            let range_numbers: Vec = range_text
                .split_ascii_whitespace()
                .map(|n| n.parse().expect("Should be a number here"))
                .collect();

            eprintln!("\trange: {:?}", range_numbers);

            let source_range = range_numbers[1]..range_numbers[1] + range_numbers[2];
            let offset = range_numbers[0] - range_numbers[1];

            eprintln!("\t\tSource range: {:?}\tOffset: {}", source_range, offset);

            // Apply the range map to the seeds
            seed_values = seed_values
                .iter()
                .map(|n| match n {
                    Value::Unmapped(n) => map_seed_range(*n, source_range.clone().into(), offset),
                    Value::Mapped(_) => vec![*n],
                })
                .flatten()
                .collect();

            eprintln!("\t\tSeed values: {:?}", seed_values);
        }

        // Reset seed values to unmapped
        seed_values = seed_values
            .iter()
            .map(|v| Value::Unmapped(v.value()))
            .collect();
    }

    // Find minimum
    let min_location = seed_values.iter().map(|v| v.min()).min().unwrap();

    println!();
    println!("Part 2: {}", min_location);
}

/// Parse string to vec of string numbers
fn parse_seeds(seeds_text: &str) -> Vec {
    seeds_text
        .split_ascii_whitespace()
        .skip(1)
        .map(|n| n.parse().expect("Should be a number here"))
        .collect()
}

/// Fill out ranges of seed numbers
fn parse_seed_ranges(seed_numbers: Vec) -> Vec> {
    seed_numbers
        .chunks(2)
        .map(|v| (v[0]..v[0] + v[1]).into())
        .collect()
}

/// Maps a seed range to possibly multiple based on a source range and offset
fn map_seed_range(seed_range: Range, source_range: Range, offset: i64) -> Vec {
    let start_cmp = seed_range.start < source_range.start;
    let end_cmp = seed_range.end <= source_range.end;

    match (start_cmp, end_cmp) {
        (false, false) => {
            if source_range.end <= seed_range.start {
                vec![Value::Unmapped(seed_range)]
            } else {
                vec![
                    Value::Mapped((seed_range.start + offset..source_range.end + offset).into()),
                    Value::Unmapped((source_range.end..seed_range.end).into()),
                ]
            }
        }
        (false, true) => vec![Value::Mapped(seed_range + offset)],
        (true, false) => vec![
            Value::Unmapped((seed_range.start..source_range.start).into()),
            Value::Mapped((source_range.start + offset..source_range.end + offset).into()),
            Value::Unmapped((source_range.end..seed_range.end).into()),
        ],
        (true, true) => {
            if seed_range.end <= source_range.start {
                vec![Value::Unmapped(seed_range)]
            } else {
                vec![
                    Value::Unmapped((seed_range.start..source_range.start).into()),
                    Value::Mapped((source_range.start + offset..seed_range.end + offset).into()),
                ]
            }
        }
    }
}