Advent of Code 2023 - Day 06

06 Dec, 2023

I'ts that time of year again, the Advent of Code! I'm completing the challenges this year using Rust 🦀 Day 6 was really chill!

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 6 Challenge

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

Solution for Part 1

use std::fs::File;
use std::io::Read;
use std::io::Result;
use std::path::Path;

use std::str::FromStr;

fn main() {
    let input_file_path = "path_to_input_file";
    let mut number_of_ways = 0;
    let mut file_as_str = read_file(input_file_path)
        .unwrap_or_else(|_| panic!("Could not find input file {}", input_file_path));
    while file_as_str.contains("  ") {
        file_as_str = file_as_str.replace("  ", " ")
    }
    let (time, distance) = file_as_str.split_once("\r\n").unwrap();
    let times = time.split(' ')
        .filter_map(|i| i32::from_str(i).ok())
        .collect::<Vec<i32>>();
    let distances = distance.split(' ')
        .filter_map(|i| i32::from_str(i).ok())
        .collect::<Vec<i32>>();

    for idx in 0..times.len() {
        let race_time = times[idx];
        let distance_to_beat = distances[idx];
        let mut winning_opportunities = 0;
        for time in 0..race_time {
            let distance = (race_time - time) * (race_time - (race_time - time));
            if distance > distance_to_beat {
                winning_opportunities += 1;
            }
        }
        if number_of_ways == 0 {
            number_of_ways = winning_opportunities;
        } else {
            number_of_ways *= winning_opportunities;
        }
    }

    println!("Number of ways to win: {}", number_of_ways);
}


fn read_file<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;
use std::io::Result;
use std::path::Path;

use std::str::FromStr;

fn main() {
    let input_file_path = "path_to_input_file";
    let mut file_as_str = read_file(input_file_path)
        .unwrap_or_else(|_| panic!("Could not find input file {}", input_file_path));
    while file_as_str.contains("  ") {
        file_as_str = file_as_str.replace("  ", " ")
    }
    let (time, distance) = file_as_str.split_once("\r\n").unwrap();
    let (_, time) = time.split_once(": ").unwrap();
    let time = i64::from_str(&time.replace(' ', "")).unwrap();
    let (_, distance) = distance.split_once(": ").unwrap();
    let distance = i64::from_str(&distance.replace(' ', "")).unwrap();

    let race_time = time;
    let distance_to_beat = distance;
    let mut winning_opportunities = 0;
    let mut last_winning_distance = 0;
    for time in 0..race_time {
        let distance = (race_time - time) * (race_time - (race_time - time));
        if distance > distance_to_beat {
            winning_opportunities += 1;
        }
        if distance < last_winning_distance && distance < distance_to_beat {
            // We have gone through all the winning combinations. Give up!
            break
        } else {
            last_winning_distance = distance;
        }
    }
    println!("Number of ways to win: {}", winning_opportunities);
}


fn read_file<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)
}