• Overview
• My Solution
• DEV Leaderboards

Overview

After my post last night, @aspittel suggested that we start a daily discussion post chain for these challenges. I think that's a neat idea, and significantly more efficient than everyone saying "Hey check out my git repo!"

I'm excited about this year's Advent mission, time traveling to save Christmas! This will be a place for discussing today's problem, Chronal Calibration. We're tasked with calibrating our time travel device by adding up sequential integers.

On a side note, if you get some extra time, it's probably a good idea to set up some infrastructure for reading input text from a file, because almost all of last year's challenges gave a few simpler examples (good for writing some basic tests) and then a huge-ish input given as a multiline plaintext file.

If you haven't solved today's puzzle yet, stop reading now, because I'm going to post my solution here. If you have finished a solution, post it in the comments! Also feel free to give (loving, instructional, nice) feedback to others' solutions to help them read better or run faster. I've seen a few people that are using this opportunity to learn a new language, so if you see something that works but isn't idiomatic to your favorite language, go ahead and offer suggestions! This includes me, since I'm just learning Rust, so I'm sure it's going to be a mixture of poorly translated Python-isms and gobbledygook.

My Solution

// day1.rs

/// Given a bunch of integers (changes in frequency), one per line,
/// calculate the final sum
pub fn final_frequency(text: &str) -> i32 {
    text.lines()
        .map(|value: &str| -> i32 {value.parse().expect("Not a number")})
        .sum()
}

/// Given a bunch of integers (changes in frequency), one per line,
/// calculate the running sum until you hit a cumulative sum that you've
/// seen before.  Return that first repeated cumulative sum.
pub fn first_duplicate_frequency(text: &str) -> i32 {
    let mut history = vec![0];
    let mut total = 0;
    for line in text.lines().cycle() {
        let value: i32 = line.parse().expect("Not a number.");
        total += value;
        if history.contains(&total) {
            return total;
        }
        history.push(total);
    }
    return 0;
}

#[cfg(test)]
mod tests {
    use super::final_frequency;
    use super::first_duplicate_frequency;

    #[test]
    fn final_all_positives() {
        assert_eq!(3, final_frequency("+1\n+1\n+1"));
    }

    // More tests...

// main.rs

// This file will change day to day as I just use it to exercise each day's module.

use std::fs::File;
use std::io::prelude::*;

mod day1;

fn main() {

    let mut input = File::open("data/day1.txt").expect("File not found.");

    let mut contents = String::new();
    input.read_to_string(&mut contents).expect("Couldn't read file.");
    println!("{}", day1::first_duplicate_frequency(&contents));
}

DEV Leaderboards

Lastly, I created a "private" leaderboard for DEV.to, in case anyone's interested. Apparently, they only hold 200 people per leaderboard, though, so first-come-first serve. Obviously, there are waaaay more than 200 people in the DEV family, so if you get there and the room is full, feel free to create your own on the Advent of Code site and post your room code in the comments. If I see somebody post a room code, I'll do my best to edit my post and copy it below, but read through the comments just in case I miss it.

Happy-- I mean, Merry Coding! I'm excited to see what people think.

@rpalo: 224198-25048a19