Adv2018/D22.1/Program.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;

namespace D22._1
{
    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]);

            int depth = int.Parse(file.ReadLine().Substring("depth: ".Length));
            int[] arrayCoord = file.ReadLine().Substring("target: ".Length).Split(",").Select(s => int.Parse(s)).ToArray();
            (int x, int y) coord = (arrayCoord[0], arrayCoord[1]);
            file.Close();

            Dictionary<(int, int), int> erosionLevels = new Dictionary<(int, int), int>();

            int risk = 0;

            for (int i = 0; i <= Math.Min(coord.x, coord.y); ++i)
            {
                for (int y = i; y <= coord.y; ++y)
                {
                    var pos = (i, y);
                    risk += ComputeRisk(coord, erosionLevels, pos, depth);
                }

                for (int x = i + 1; x <= coord.x; ++x)
                {
                    var pos = (x, i);
                    risk += ComputeRisk(coord, erosionLevels, pos, depth);
                }
            }

            Console.WriteLine($"Total risk is : {risk}");
        }

        private static int ComputeRisk((int x, int y) coord, Dictionary<(int, int), int> erosionLevels, (int x, int y) pos, int depth)
        {
            int geo = 0;
            if (pos != (0, 0) && pos != coord)
            {
                if (pos.x == 0) geo = pos.y * 48271;
                else if (pos.y == 0) geo = pos.x * 16807;
                else geo = erosionLevels[(pos.x - 1, pos.y)] * erosionLevels[(pos.x, pos.y - 1)];
            }

            int ero = (geo + depth) % 20183;
            int type = ero % 3;

            erosionLevels.Add(pos, ero);
            return type;
        }
    }
}