2015 day 9

2015/aoc2015/HelperFunctions.cs

@@ -17,20 +17,20 @@ public string[] ReadRealInput(int day, bool example = false) {
 
     public static void Main() {
         Console.Write("Day to Run: ");
-        if (int.TryParse(Console.ReadLine(), out var day)) {
-            var days = new Dictionary<int, Action> {
-                { 1, () => new Day1().Run() },
-                { 2, () => new Day2().Run() },
-                { 3, () => new Day3().Run() },
-                { 4, () => new Day4().Run() },
-                { 5, () => new Day5().Run() },
-                { 6, () => new Day6().Run() },
-                { 7, () => new Day7().Run() },
-                { 8, () => new Day8().Run() }
-            };
-            if (days.TryGetValue(day, out var action)) {
-                action(); // Run the corresponding day's logic
-            }
+        if (!int.TryParse(Console.ReadLine(), out var day)) return;
+        var days = new Dictionary<int, Action> {
+            { 1, () => new Day1().Run() },
+            { 2, () => new Day2().Run() },
+            { 3, () => new Day3().Run() },
+            { 4, () => new Day4().Run() },
+            { 5, () => new Day5().Run() },
+            { 6, () => new Day6().Run() },
+            { 7, () => new Day7().Run() },
+            { 8, () => new Day8().Run() },
+            { 9, () => new Day9().Run() }
+        };
+        if (days.TryGetValue(day, out var action)) {
+            action(); // Run the corresponding day's logic
         }
     }
 }

2015/aoc2015/day9.cs

@@ -0,0 +1,73 @@
+// Nelson Dane
+// Advent of Code 2015 Day 9
+
+namespace aoc2015;
+
+public class Day9 {
+    // https://stackoverflow.com/a/12249225
+    private static IEnumerable<IEnumerable<T>> GetPermutations<T>(IEnumerable<T> items, int count) {
+        // Unique permutations
+        var i = 0;
+        foreach (var item in items) {
+            if (count == 1) {
+                yield return new T[] { item };
+            }
+            else {
+                foreach (var result in GetPermutations(items.Except(new[] { item }), count - 1)) {
+                    yield return new T[] { item }.Concat(result);
+                }
+            }
+            i++;
+        }
+    }
+
+    private static void Part1() {
+        var helpers = new HelperFunctions();
+        var input = helpers.ReadRealInput(day: 9, example: false);
+        var distancesList = new List<(string, string, int)>();
+        foreach (var line in input) {
+            var distance = line.Split(" = ");
+            var cities = distance[0].Split(" to ");
+            distancesList.Add((cities[0], cities[1], int.Parse(distance[1])));
+        }
+        // Get all cities from Item1 + Item2 then dedupe
+        var citiesList = distancesList.Select(x => x.Item1).ToList();
+        citiesList.AddRange(distancesList.Select(x => x.Item2).ToList());
+        citiesList = citiesList.Distinct().ToList();
+        // Get all combinations
+        var allPermutations = GetPermutations(citiesList, citiesList.Count);
+        var listPerms = allPermutations.Select(x => x.ToList()).ToList();
+        var shortestRoute = int.MaxValue; // lol
+        var longestRoute = 0;
+        foreach (var route in listPerms) {
+            var routeDistance = 0;
+            var possiblePerm = true;
+            for (var i = 0; i < route.Count - 1; i++) {
+                var city1 = route[i];
+                var city2 = route[i + 1];
+                // Find the distance
+                var found = false;
+                foreach (var distance in distancesList) {
+                    if ((distance.Item1 == city1 && distance.Item2 == city2) || (distance.Item1 == city2 && distance.Item2 == city1)) {
+                        routeDistance += distance.Item3;
+                        found = true;
+                    }
+                }
+                if (found) continue;
+                // Invalid route, impossible perm
+                possiblePerm = false;
+                break;
+            }
+            // End loop calculations
+            if (!possiblePerm) break;
+            if (routeDistance < shortestRoute) shortestRoute = routeDistance;
+            if (routeDistance > longestRoute) longestRoute = routeDistance;
+        }
+        Console.WriteLine($"Part 1 Shortest: {shortestRoute}");
+        Console.WriteLine($"Part 2 Longest: {longestRoute}");
+    }
+
+    public void Run() {
+        Part1();
+    }
+}