lotto/src/main.rs

use anyhow::anyhow;
use std::io::BufRead;
use std::{
    io::{stdin, BufReader},
    time::Instant,
};

type Ticket = [u8; 5];
const NUM_ENTRIES: usize = 10_000_000;

fn ticket_from_str(s: &str) -> Result<Ticket, anyhow::Error> {
    let mut nums = s.split(" ").take(5).map(|s| s.parse::<u8>()).into_iter();

    let num1 = nums.next();
    let num2 = nums.next();
    let num3 = nums.next();
    let num4 = nums.next();
    let num5 = nums.next();
    if num1.is_none() || num2.is_none() || num3.is_none() || num4.is_none() || num5.is_none() {
        return Err(anyhow!("invalid lotto number"));
    }
    let r = [
        num1.unwrap()?,
        num2.unwrap()?,
        num3.unwrap()?,
        num4.unwrap()?,
        num5.unwrap()?,
    ];

    if r[0] < 1
        || r[1] < 1
        || r[2] < 1
        || r[3] < 1
        || r[4] < 1
        || r[0] > 90
        || r[1] > 90
        || r[2] > 90
        || r[3] > 90
        || r[4] > 90
    {
        return Err(anyhow!("lotto number too high"));
    }

    Ok(r)
}

fn num_matches(t1: Ticket, t2: Ticket) -> usize {
    let mut result = 0;
    for n1 in t1 {
        for n2 in t2 {
            if n1 == n2 {
                result += 1;
            }
        }
    }
    result
}

fn main() -> Result<(), anyhow::Error> {
    println!("Parsing entries");

    let reader = BufReader::new(stdin());
    let mut entries = Vec::with_capacity(NUM_ENTRIES);

    for line in reader.lines() {
        match line {
            Ok(l) => match ticket_from_str(&l) {
                Ok(n) => entries.push(n),
                Err(_) => {} // noop
            },
            Err(_) => break,
        }
    }
    println!("{} entries parsed from stdin", entries.len());

    let winning = [68, 81, 40, 34, 85];

    let start = Instant::now();
    println!("Counting winners... (timer started)");
    let mut winners: [usize; 6] = [0, 0, 0, 0, 0, 0];

    for n in entries {
        let num_winning = num_matches(n, winning);
        winners[num_winning] += 1
    }

    println!("Done counting winners (timer stopped)");
    let duration = start.elapsed();

    println!(
        "Winners: {:?}\nTime Elapsed: {}ms",
        winners,
        duration.subsec_millis()
    );

    Ok(())
}