use std::{collections::HashSet, fs::read_to_string};

fn find_nonrecuring_sequence(input: &[char], length: usize) -> usize {
    input
        .windows(length)
        .enumerate()
        .find(|(_, chars)| chars.iter().collect::<HashSet<_>>().len() == length)
        .unwrap_or((input.len(), &[]))
        .0
        + length
}

fn main() {
    const PACKET_START_LENGTH: usize = 4;
    const MESSAGE_START_LENGTH: usize = 14;
    let input = read_to_string("input.txt").unwrap();
    let input = input.chars().collect::<Vec<_>>();
    let packet_marker = find_nonrecuring_sequence(&input, PACKET_START_LENGTH);
    println!("first packet marker at {packet_marker}");
    let message_marker = find_nonrecuring_sequence(&input, MESSAGE_START_LENGTH);
    println!("first message marker at {message_marker}");
}