Advent of Code 2023 - Day 09

09 Dec, 2023

I'ts that time of year again, the Advent of Code! I'm completing the challenges this year using Rust 🦀 Day 9 was smooth sailing!

I'll be posting them here, just to document how I'm solving each challenge, and I highly encourage you to check them out before reading my solutions!

Here's the Day 9 Challenge

BTW: Complete Part 1 to have access to Part 2 😉

Solution for Part 1

use std::fs::File;
use std::io::{Read, Result};
use std::path::Path;
use std::str::FromStr;

fn main() {
    let input_file_path = "path_to_file";
    let mut curr_sum = 0;
    let file = file_as_string(input_file_path)
        .unwrap_or_else(|_| panic!("Could not find input file {}", input_file_path));
    for line in file.split("\r\n") {
        let mut histories : Vec<Vec<i64>> = vec![];
        let history_vec = line.split(' ').map(|i| i64::from_str(i).unwrap()).collect::<Vec<i64>>();
        histories.push(history_vec);

        while !histories.last().unwrap().iter().all(|i| i == &0) {
            let last_row = histories.last().unwrap();
            let mut new_row: Vec<i64> = vec![];
            for window in last_row.windows(2) {
                new_row.push(window[1] - window[0]);
            }
            histories.push(new_row);
        }
        histories.reverse();
        let mut results : Vec<i64> = vec![0];
        for (idx, _) in histories.as_slice().iter().enumerate() {
            if histories.len() == idx + 1 {
                continue
            }
            let last_el = results.last().unwrap();
            let last_el_next_row = histories.get(idx + 1).unwrap().last().unwrap();
            results.push(last_el + last_el_next_row);
        }
        curr_sum += results.last().unwrap();
    }
    println!("Sum of all last extrapolated values: {}", curr_sum);
}

fn file_as_string<P: AsRef<Path>>(filename: P) -> Result<String> {
    let mut file = File::open(filename)?;
    let mut file_as_str = String::new();
    File::read_to_string(&mut file, &mut file_as_str)?;
    Ok(file_as_str)
}

Solution for Part 2

use std::fs::File;
use std::io::{Read, Result};
use std::path::Path;
use std::str::FromStr;

fn main() {
    let input_file_path = "path_to_input_file";
    let mut curr_sum = 0;
    let file = file_as_string(input_file_path)
        .unwrap_or_else(|_| panic!("Could not find input file {}", input_file_path));
    for line in file.split("\r\n") {
        let mut histories : Vec<Vec<i64>> = vec![];
        let history_vec = line.split(' ').map(|i| i64::from_str(i).unwrap()).collect::<Vec<i64>>();
        histories.push(history_vec);

        while !histories.last().unwrap().iter().all(|i| i == &0) {
            let last_row = histories.last().unwrap();
            let mut new_row: Vec<i64> = vec![];
            for window in last_row.windows(2) {
                new_row.push(window[1] - window[0]);
            }
            histories.push(new_row);
        }
        histories.reverse();
        let mut results : Vec<i64> = vec![0];
        for (idx, _) in histories.as_slice().iter().enumerate() {
            if histories.len() == idx + 1 {
                continue
            }
            let last_el = results.last().unwrap();
            // Only lines that actually differ are these 2 :P
            let last_el_next_row = histories.get(idx + 1).unwrap().first().unwrap();
            results.push(last_el_next_row - last_el);
        }
        curr_sum += results.last().unwrap();
    }
    println!("Sum of all last extrapolated values: {}", curr_sum);
}

fn file_as_string<P: AsRef<Path>>(filename: P) -> Result<String> {
    let mut file = File::open(filename)?;
    let mut file_as_str = String::new();
    File::read_to_string(&mut file, &mut file_as_str)?;
    Ok(file_as_str)
}