Advent of Code 2021 - day 2

day2-part1.cs

// Advent of Code 2021, day 2, part 1.
// Solved using funny immutable and functional C#.
// Written by Jämes Ménétrey.
using System;
using System.IO;
using System.Linq;

var result = File.ReadAllLines("input.txt")
        .Aggregate(new Submarine(), ParseInput, submarine => submarine.Result);
Console.WriteLine($"Result: {result}");

Submarine ParseInput(Submarine submarine, string input)
{
    var (movement, x) = input.Split(' ') switch
    {
        var split when split.Length == 2 => (split[0], int.Parse(split[1])),
        var split => throw new Exception($"The input '{split}' is invalid.")
    };

    return movement switch
    {
        "forward" => submarine.Forward(x),
        "down" => submarine.Down(x),
        "up" => submarine.Up(x),
        _ => throw new Exception($"The action '{movement}' is not recognized.")
    };
}

record Submarine(int Horizontal = 0, int Depth = 0)
{
    public Submarine Forward(int x) => this with { Horizontal = Horizontal + x };
    public Submarine Down(int x) => this with { Depth = Depth + x };
    public Submarine Up(int x) => this with { Depth = Depth - x };
    public int Result => Horizontal * Depth;
}

day2-part2.cs

// Advent of Code 2021, day 2, part 2.
// Solved using funny immutable and functional C#.
// Written by Jämes Ménétrey.
using System;
using System.IO;
using System.Linq;

var result = File.ReadAllLines("input.txt")
        .Aggregate(new Submarine(), ParseInput, submarine => submarine.Result);
Console.WriteLine($"Result: {result}");

Submarine ParseInput(Submarine submarine, string input)
{
    var (movement, x) = input.Split(' ') switch
    {
        var split when split.Length == 2 => (split[0], int.Parse(split[1])),
        var split => throw new Exception($"The input '{split}' is invalid.")
    };

    return movement switch
    {
        "forward" => submarine.Forward(x),
        "down" => submarine.Down(x),
        "up" => submarine.Up(x),
        _ => throw new Exception($"The action '{movement}' is not recognized.")
    };
}

record Submarine(int Horizontal = 0, int Depth = 0, int Aim = 0)
{
    public Submarine Forward(int x) => this with { Horizontal = Horizontal + x, Depth = Depth + Aim * x };
    public Submarine Down(int x) => this with { Aim = Aim + x };
    public Submarine Up(int x) => this with { Aim = Aim - x };
    public int Result => Horizontal * Depth;
}