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Nicky Meuleman
Nicky Meuleman

Posted on • Originally published at nickymeuleman.netlify.app

Advent of Code 2022 Day 1

Day 1: Calorie Counting

https://adventofcode.com/2022/day/1

TL;DR: my solution in Rust

We're on an expedition with the elves.
The input file represents the amount of calories each elf carries with them.
Each elf has several items.
The inventories of each elf is seperated by two line breaks.

1000
2000
3000

4000

5000
6000

7000
8000
9000

10000
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Part 1

Find the Elf carrying the most Calories.
How many total Calories is that Elf carrying?

For each elf we want to calculate the sum of the items they are carrying.
Then, find the largest of those sums.

I did today with one iterator chain.

Get the input string.
Split it on double newlines.
Each iterator element is now a string that represents the inventory of a single elf.

For every element: split on a single linebreak.
Turn that line into a number.
Take the sum of every number.

Now, every element is the sum a single elf is carrying.
Find the maximum of those sums.

pub fn part_1() -> u32 {
    let input = std::fs::read_to_string("src/day01.txt").unwrap();

    input
    .split("\n\n")
    .map(|elf| {
        elf.lines()
            .filter_map(|s| s.parse::<u32>().ok())
            .sum::<u32>()
    })
    .max()
    .unwrap()
}
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Part 2

Part 2 is very similar.

Find the top three Elves carrying the most Calories.
How many Calories are those Elves carrying in total?

Get the input string.
Split it on double newlines.
Each iterator element is now a string that represents the inventory of a single elf.

For every element: split on a single linebreak.
Turn that line into a number.
Take the sum of every number.

Now, every element is the sum a single elf is carrying.
Sort those sums.
Take the 3 largest sums, and sum those.

To sort the iterator directly, I used the sorted() method from the itertools crate.
I could have also called .collect() on the iterator of all sums, and store that result in a variable with type Vec<u32>.
Then sort that resulting vector with .sort().

This sorts in ascending order, and I want the sum of the 3 last ones.
So I reverse the iterator.
Take 3 items of that iterator.
Sum those.

use itertools::Itertools;

pub fn part_2() -> u32 {
    let input = std::fs::read_to_string("src/day01.txt").unwrap();

    input
    .split("\n\n")
    .map(|elf| {
        elf.lines()
            .filter_map(|s| s.parse::<u32>().ok())
            .sum::<u32>()
    })
    .sorted()
    .rev()
    .take(3)
    .sum::<u32>()
}
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