use std::collections::HashMap;
use std::error::Error;
use std::fs::File;
use std::io::{self, BufRead};
use std::vec::Vec;

fn main() -> Result<(), Box<dyn Error>> {
    let file = File::open("inputs/day15.txt")?;
    let mut lines = io::BufReader::new(file).lines();

    let starting_numbers: Vec<u32> = lines
        .nth(0)
        .unwrap()
        .unwrap()
        .split(',')
        .map(|n| n.parse().unwrap())
        .collect();

    let mut last_occurences: HashMap<u32, u32> = HashMap::new();

    let mut last_number = *starting_numbers.first().unwrap();
    for turn in 1..30000001 {
        let spoken_number = if turn <= starting_numbers.len() {
            starting_numbers[turn - 1]
        } else if last_occurences.contains_key(&last_number) {
            turn as u32 - last_occurences[&last_number]
        } else {
            0
        };

        last_occurences.insert(last_number, turn as u32);
        //println!("Spoken number {} : {}", turn, spoken_number);
        last_number = spoken_number;
    }

    println!("Last Number: {}", last_number);

    Ok(())
}