I built a framework yesterday to waaaaaaay overdesign handling these instead of my normal per-problem-program style, unsure why, but it’s fun and I get great CLI help, lol. It’s available at:

2021-01 is at:

The first part of the function is just opening the file and parsing it with way too much error checking (which is entirely unnecessary for an AoC, but again, overdesigned, lol). The part that solves each part is just (nums is the array of integers, yes I know I could have solved them while parsing without storing anything, and I did that originally, but I like how pretty this even if a couple microseconds slower, lol):

		println!(
			"Step 1: {}",
			nums.iter()
				.tuple_windows()
				.map(|(a, b)| a < b)
				.filter(|&x| x)
				.count()
		);
		println!(
			"Step 2: {}",
			nums.iter()
				.tuple_windows()
				.map(|(a, b, c)| a + b + c)
				.tuple_windows()
				.map(|(a, b)| a < b)
				.filter(|&x| x)
				.count()
		);

And my result times:

❯ cargo run --release -- -v 2021 1 ./inputs/2021/day1.input
   Compiling advent_of_code v0.1.0 (/home/overminddl1/rust/advent_of_code)
    Finished release [optimized] target(s) in 14.08s
     Running `target/release/advent_of_code -v 2021 1 ./inputs/2021/day1.input`
AocApp { verbose: 1, command: Run(Year2021 { day: Day1(Day1 { input_file: "./inputs/2021/day1.input" }) }) }
Step 1: 1448
Step 2: 1471
Time Taken: 97.823µs

(The original version that didn’t store the integers and rather just calculated as it went was at just over 92µs, so that’s the extra cost of the allocations and such.)

EDIT1: Broke out the file reading/parsing code into a standalone module for all the tasks to share (my all generic helpers name, lol), so now my complete 2021-01 code is now:

use crate::aoc::helpers::*;
use clap::Parser;
use itertools::Itertools;
use std::path::PathBuf;

#[derive(Debug, Parser)]
pub struct Day1 {
	/// The input file of "depths"
	pub input_file: PathBuf,
}

impl Day1 {
	pub fn run(&self) -> anyhow::Result<()> {
		let nums =
			map_trimmed_nonempty_lines_of_file(
				&self.input_file,
				|line| Ok(line.parse::<usize>()?),
			)?;
		println!(
			"Step 1: {}",
			nums.iter()
				.tuple_windows()
				.map(|(a, b)| a < b)
				.filter(|&x| x)
				.count()
		);
		println!(
			"Step 2: {}",
			nums.iter()
				.tuple_windows()
				.map(|(a, b, c)| a + b + c)
				.tuple_windows()
				.map(|(a, b)| a < b)
				.filter(|&x| x)
				.count()
		);

		Ok(())
	}
}

EDIT2: And by pretty help messages I mean like this:

❯ ./target/release/advent_of_code 2021 1 --help                
advent_of_code-2021-1 

Advent of Code 2021, Day 1 - Sonar Sweep

USAGE:
    advent_of_code 2021 1 <INPUT_FILE>

ARGS:
    <INPUT_FILE>    The input file of "depths"

OPTIONS:
    -h, --help    Print help information

Each year and day are a command subtask as well, so each has it’s own help too:

❯ ./target/release/advent_of_code 2021 --help  
advent_of_code-2021 

Advent of Code 2021

USAGE:
    advent_of_code 2021 <SUBCOMMAND>

OPTIONS:
    -h, --help    Print help information

SUBCOMMANDS:
    1       Advent of Code 2021, Day 1 - Sonar Sweep
    help    Print this message or the help of the given subcommand(s)

And the top-most help:

❯ ./target/release/advent_of_code --help     
advent_of_code 

USAGE:
    advent_of_code [OPTIONS] <SUBCOMMAND>

OPTIONS:
    -h, --help       Print help information
    -v, --verbose    Level of verbosity, can be used multiple times for more verbosity

SUBCOMMANDS:
    2015    Advent of Code 2015
    2016    Advent of Code 2016
    2017    Advent of Code 2017
    2018    Advent of Code 2018
    2019    Advent of Code 2019
    2020    Advent of Code 2020
    2021    Advent of Code 2021
    help    Print this message or the help of the given subcommand(s)
    tui

(It’s far more pretty in the terminal with it’s colorization and all too)

Like I said, waaaaaaay overdesigned this, lol.

EDIT3: Added ability to run all known solutions with the default inputs in the input directory, and the output:

Year2015

Year2015 Time Taken: 70ns

Year2016

Year2016 Time Taken: 70ns

Year2017

Year2017 Time Taken: 70ns

Year2016

Year2016 Time Taken: 70ns

Year2019

Year2019 Time Taken: 80ns

Year2020

Day1

Step 1: 731731
Step 2: 116115990
Day1 Time Taken: 187.376µs

Day2

Step 1: 515
Step 2: 711
Day2 Time Taken: 485.364µs
Year2020 Time Taken: 709.758µs

Year2021

Day1

Step 1: 1448
Step 2: 1471
Day1 Time Taken: 239.692µs
Year2021 Time Taken: 253.871µs
All Time Taken: 1.005027ms

(The times are because I have verbose mode showing with -v.)

Well, then maybe also LFE would be worth a try?

Advent of Code Day 1 completed. Took me 3 minutes to complete yet I did not get a position in the leaderboard.

I started with Elixir, then went ahead and did F# as well.

The Elixir one:

defmodule AdventOfCode.Y2021.Day01 do
  @moduledoc """
  --- Day 1: Sonar Sweep ---
  Problem Link: https://adventofcode.com/2021/day/1
  """
  use AdventOfCode.Helpers.InputReader, year: 2021, day: 1

  def run_1, do: input!() |> parse() |> depth_increase()
  def run_2, do: input!() |> parse() |> sliding_window() |> depth_increase()

  def parse(data) do
    data
    |> String.split("\n")
    |> Enum.map(&String.to_integer/1)
  end

  defp depth_increase(measurements) do
    measurements
    |> Enum.chunk_every(2, 1, :discard)
    |> Enum.count(fn [a, b] -> b - a > 0 end)
  end

  defp sliding_window(measurements) do
    measurements
    |> Enum.chunk_every(3, 1, :discard)
    |> Enum.map(&Enum.sum/1)
  end
end

The F# One:

/// Advent of Code 2021
/// Day 1: Sonar Sweep
/// Description: https://adventofcode.com/2021/day/1
module Year2021Day01

open AdventOfCode.FSharp.Utils

module Solution =
    let increase =
        Seq.pairwise
        >> Seq.filter (fun (a, b) -> b - a > 0)
        >> Seq.length

    let solvePart1 = ints >> increase >> output

    let solvePart2 =
        let slidingWindow =
            Seq.pairwise
            >> Seq.pairwise
            >> Seq.map (fun ((a, b), (_, d)) -> a + b + d)

        ints >> slidingWindow >> increase >> output

    let solve (input: string seq) = (solvePart1 input, solvePart2 input)