Program.cs

using AdventOfCode.Interfaces;
using System;
using System.Diagnostics;
using System.IO;

namespace AdventOfCode
{
    class Program
    {
        private const int DayToSolve = 25;

        static void Main(string[] args)
        {
            // Create solver
            var solverTypeName = "AdventOfCode.Day" + DayToSolve.ToString("D2");
            var solverType = Type.GetType(solverTypeName);
            if (solverType == null)
            {
                Console.WriteLine($"Invalid type: {solverTypeName}");
                return;
            }
            var solver = Activator.CreateInstance(solverType) as ISolver;

            // Read first input file
            var firstStarFilePath = Path.Combine(solver.GetType().Name, solver.InputFileName);
            var firstStarFileReader = File.OpenText(firstStarFilePath);

            var stopWatch = Stopwatch.StartNew();
            var firstStarResult = solver.SolveFirstStar(firstStarFileReader);
            stopWatch.Stop();
            Console.WriteLine($"First star result: {firstStarResult}, {stopWatch.ElapsedMilliseconds}ms");

            // Read second input file
            var secondStarFilePath = Path.Combine(solver.GetType().Name, solver.InputFileName);
            var secondStarFileReader = File.OpenText(secondStarFilePath);

            stopWatch.Reset();
            stopWatch.Start();
            var secondStarResult = solver.SolveSecondStar(secondStarFileReader);
            stopWatch.Stop();
            Console.WriteLine($"Second star result: {secondStarResult}, {stopWatch.ElapsedMilliseconds}ms");
        }
    }
}