AdventOfCode/Days/Day3.cs

using Spectre.Console;

namespace AdventOfCode.Days;

public class Day3 : Day
{
    public override int Number => 3;
    public override string Name => "Lobby";

    public override void RunPart1(bool display = true)
    {
        var totalOutputJoltage = 0L;

        Span<int> bank = stackalloc int[100];

        foreach (var line in Input.EnumerateLines())
        {
            // Parse the line into battery values
            for (var i = 0; i < bank.Length; i++)
            {
                bank[i] = line[i] - '0';
            }

            // The first digit the joltage value will be the "left-most" biggest number we can find
            var firstDigitMax = bank[0];
            var firstDigitMaxIndex = 0;

            for (var i = 1; i < bank.Length - 1; i++)
            {
                var batteryValue = bank[i];
                if (batteryValue > firstDigitMax)
                {
                    firstDigitMax = batteryValue;
                    firstDigitMaxIndex = i;

                    // We cannot have a digit bigger than 9
                    if (batteryValue is 9)
                    {
                        break;
                    }
                }
            }

            // Now we can find the second digit which will be the biggest digit on the right of the first one
            var secondDigitMax = bank[firstDigitMaxIndex + 1];
            for (var i = firstDigitMaxIndex + 2; i < bank.Length; i++)
            {
                var batteryValue = bank[i];

                if (batteryValue > secondDigitMax)
                {
                    secondDigitMax = batteryValue;

                    if (batteryValue is 9)
                    {
                        break;
                    }
                }
            }

            // Build the joltage value
            totalOutputJoltage += firstDigitMax * 10 + secondDigitMax;
        }

        if (display)
        {
            AnsiConsole.MarkupLine($"[green]The total output joltage is: [yellow]{totalOutputJoltage}[/][/]");
        }
    }

    public override void RunPart2(bool display = true)
    {
        var totalOutputJoltage = 0L;

        Span<int> bank = stackalloc int[100];

        foreach (var line in Input.EnumerateLines())
        {
            // Parse the line into battery values
            for (var i = 0; i < bank.Length; i++)
            {
                bank[i] = line[i] - '0';
            }

            var maxIndex = -1;
            for (var digitPosition = 11; digitPosition >= 0; digitPosition--)
            {
                // Next max is always on the right of previous one
                maxIndex++;

                // Find biggest battery value on the right
                var max = bank[maxIndex];
                for (var i = maxIndex + 1; i < bank.Length - digitPosition; i++)
                {
                    var batteryValue = bank[i];

                    if (batteryValue > max)
                    {
                        maxIndex = i;
                        max = batteryValue;

                        // We cannot have a digit bigger than 9
                        if (batteryValue is 9)
                        {
                            break;
                        }
                    }
                }

                // Directly add its value to the total, we don't need to do compound sum
                totalOutputJoltage += max * (long) Math.Pow(10, digitPosition);
            }
        }

        if (display)
        {
            AnsiConsole.MarkupLine($"[green]The total output joltage is: [yellow]{totalOutputJoltage}[/][/]");
        }
    }
}