Adv2018/D5.2/Program.cs

using System;
using System.IO;
using System.Linq;

namespace D5._2
{
    class Program
    {
        static void Main(string[] args)
        {
            if (args.Length < 1) return;
            if (File.Exists(args[0]) == false) return;

            var file = File.OpenText(args[0]);

            string polymer = file.ReadLine();

            int shortest = polymer.Length;
            for (char i = 'A'; i <= 'Z'; i++)
            {
                var altera = alterPolymer(polymer, i);
                reduce(ref altera);

                if (altera.Length < shortest) shortest = altera.Length;
            }

            Console.WriteLine(shortest);
        }

        static void reduce(ref string polymer)
        {
            for (int i = 1; i < polymer.Length; i++)
            {
                char cc = polymer[i];
                char cm = polymer[i - 1];

                if (Math.Abs(cc - cm) <= 26) continue;
                if (up(cc) == up(cm))
                {
                    polymer = polymer.Remove(i - 1, 2);
                    i = Math.Max(0, i - 2);
                }
            }
        }

        static string alterPolymer(string polymer, char unit)
        {
            string newPolymer = string.Empty;
            foreach (var car in polymer)
            {
                if (up(car) == up(unit)) continue;
                newPolymer += car;
            }
            return newPolymer;
        }

        static char up(char c)
        {
            if (c >= 'A' && c <= 'Z') return c;
            return (char)('A' + (c - 'a'));
        }
    }
}