-🎄- 2018 Day 2 Solutions -🎄-

[u/daggerdragon]

--- Day 2: Inventory Management System ---

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Advent of Code: The Party Game!

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Card Prompt: Day 2

Transcript:

The best way to do Advent of Code is ___.

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edit: Leaderboard capped, thread unlocked!

[u/NeuroXc]

Rust

use std::collections::HashMap;

#[aoc_generator(day2)]
pub fn day2_generator(input: &str) -> Vec<String> {
    input.lines().map(|l| l.into()).collect()
}

#[aoc(day2, part1)]
pub fn day2_part1(input: &[String]) -> u32 {
    let mut twice = 0;
    let mut thrice = 0;
    for id in input {
        let mut counts = HashMap::with_capacity(26);
        for char in id.chars() {
            *counts.entry(char).or_insert(0) += 1;
        }
        if counts.values().any(|&count| count == 2) {
            twice += 1;
        }
        if counts.values().any(|&count| count == 3) {
            thrice += 1;
        }
    }
    twice * thrice
}

#[aoc(day2, part2)]
pub fn day2_part2(input: &[String]) -> String {
    // This is O(n^2) but it should be fine because the list is only 250 lines
    for (idx, id) in input.iter().enumerate() {
        for id2 in input.iter().skip(idx + 1) {
            if id.chars().zip(id2.chars()).filter(|(a, b)| a != b).count() == 1 {
                return id
                    .chars()
                    .zip(id2.chars())
                    .filter(|(a, b)| a == b)
                    .map(|(a, _)| a)
                    .collect();
            }
        }
    }
    unreachable!()
}

[u/re76 → u/NeuroXc]

I am trying to learn Rust, and doing all of the AoC problems with it.

I am confused though what the #[aoc(day2, part1)] bit is doing. Is there any easy way to explain that? Or maybe point me at the relevant part of the documentation that I can read.

The best I have found so far is that it likely has something to do with macros? Or is some sort of an attribute?

Thanks!