src/bin/1.rs


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use std::{
    collections::HashMap,
    error::Error,
    fs::File,
    io::{BufRead, BufReader},
};

fn main() -> Result<(), Box<dyn Error>> {
    let f = File::open("input/1")?;
    let f = BufReader::new(f);
    let mut list_a: Vec<i64> = Vec::new();
    let mut list_b: Vec<i64> = Vec::new();
    for line in f.lines() {
        let line = line?;
        let (a, b) = line.trim_end().split_once("   ").ok_or("Invalid line")?;
        list_a.push(a.parse()?);
        list_b.push(b.parse()?);
    }
    list_a.sort();
    list_b.sort();
    println!(
        "part1: {}",
        list_a
            .iter()
            .zip(list_b.iter())
            .map(|p| (p.0 - p.1).abs())
            .sum::<i64>()
    );
    let mut frequencies: HashMap<i64, i64> = HashMap::new();
    for n in list_b {
        *frequencies.entry(n).or_default() += 1;
    }
    println!(
        "part2: {}",
        list_a
            .into_iter()
            .map(|n| n * frequencies.get(&n).copied().unwrap_or_default())
            .sum::<i64>()
    );
    Ok(())
}