Adding Day 3 Solution

csharp/Day3Solution.cs

@@ -0,0 +1,96 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+
+namespace AOC2015
+{
+    class Day3Solution : Solution
+    {
+        public override int Day => 3;
+        public override string Name => "Day 3: Perfectly Spherical Houses in a Vacuum";
+
+        public override void Run()
+        {
+            string input = File.ReadAllText("Input\\Day3Input.txt");
+
+            Console.WriteLine($"Part 1 Answer Example 1: {Part1("^v")}");
+            Console.WriteLine($"Part 1 Answer Example 2: {Part1("^>v<")}");
+            Console.WriteLine($"Part 1 Answer Example 3: {Part1("^v^v^v^v^v")}");
+            Console.WriteLine($"Part 1 Answer: {Part1(input)}");
+
+            Console.WriteLine($"Part 2 Answer Example 1: {Part2("^v")}");
+            Console.WriteLine($"Part 2 Answer Example 2: {Part2("^>v<")}");
+            Console.WriteLine($"Part 2 Answer Example 3: {Part2("^v^v^v^v^v")}");
+            Console.WriteLine($"Part 2 Answer: {Part2(input)}");
+        }
+
+        private int Part1(string input)
+        {
+            int x = 0, y = 0;
+            Dictionary<string, int> visitLog = new Dictionary<string, int>();
+
+            visitLog.Add("0,0",1); // starting position gets a present
+            for (int i = 0; i < input.Length; i++)
+            {
+                if (input[i] == '<')
+                    x--;
+                else if (input[i] == '>')
+                    x++;
+                else if (input[i] == '^')
+                    y++;
+                else if (input[i] == 'v')
+                    y--;
+
+                var key = $"{x},{y}";
+                if (visitLog.ContainsKey(key))
+                    visitLog[key]++;
+                else
+                    visitLog.Add(key, 1);
+            }
+            return visitLog.Count;
+        }
+
+        private int Part2(string input)
+        {
+            int x = 0, y = 0, robo_x = 0, robo_y = 0;
+            Dictionary<string, int> visitLog = new Dictionary<string, int>();
+
+            visitLog.Add("0,0", 2); // starting position gets 2 presents
+            for (int i = 0; i < input.Length; i++)
+            {
+                if (i % 2 == 0)
+                {
+                    // Santa
+                    if (input[i] == '<')
+                        x--;
+                    else if (input[i] == '>')
+                        x++;
+                    else if (input[i] == '^')
+                        y++;
+                    else if (input[i] == 'v')
+                        y--;
+                }
+                else
+                {
+                    // Robo-Santa
+                    if (input[i] == '<')
+                        robo_x--;
+                    else if (input[i] == '>')
+                        robo_x++;
+                    else if (input[i] == '^')
+                        robo_y++;
+                    else if (input[i] == 'v')
+                        robo_y--;
+                }
+
+                var key = (i % 2 == 0 ? $"{x},{y}" : $"{robo_x},{robo_y}");
+                if (visitLog.ContainsKey(key))
+                    visitLog[key]++;
+                else
+                    visitLog.Add(key, 1);
+            }
+            return visitLog.Count;
+        }
+    }
+}