2022 Day 6

use std::env;
use std::io::{self};
use std::collections::HashSet;

fn packet_start(s: &str) -> usize {
    const MARKER_SIZE: usize = 4;
    let mut start = MARKER_SIZE;
    for chs in s.chars().collect::<Vec<_>>().windows(MARKER_SIZE) {
        let (a,b,c,d) = (chs[0],chs[1],chs[2],chs[3]);
        if a != b && a != c && a != d && b != c && b != d && c != d { break }
        else { start += 1; }
    }
    start
}

fn message_start(s: &str) -> usize {
    const MARKER_SIZE: usize = 14;
    let mut start = MARKER_SIZE;
    'outer: for chs in s.chars().collect::<Vec<_>>().windows(MARKER_SIZE) {
        start += 1;
        let mut char_set: HashSet<char> = HashSet::new();
        for ch in chs {
            if char_set.contains(ch) { continue 'outer; }
            else { char_set.insert(*ch); }
        }
        break;
    }
    start - 1
}

fn solve(input: &str) -> io::Result<()> {
    // Input
    let input_str = std::fs::read_to_string(input).unwrap();
    let input_str = input_str.trim();

    // Output
    println!("Part 1: {}",packet_start(input_str)); // 1578
    println!("Part 2: {}",message_start(input_str)); // 2178

    Ok(())
}

fn main() {
    let args: Vec<String> = env::args().collect();
    let filename = &args[1];
    solve(&filename).unwrap();
}