Data commit

Task/Ludic-numbers/C-sharp/ludic-numbers.cs

@@ -0,0 +1,68 @@
+using System;
+using System.Linq;
+using System.Collections.Generic;
+
+public class Program
+{
+    public static void Main()
+    {
+        Console.WriteLine("First 25 ludic numbers:");
+        Console.WriteLine(string.Join(", ", LudicNumbers(150).Take(25)));
+        Console.WriteLine();
+
+        Console.WriteLine($"There are {LudicNumbers(1001).Count()} ludic numbers below 1000");
+        Console.WriteLine();
+
+        foreach (var ludic in LudicNumbers(22000).Skip(1999).Take(6)
+                .Select((n, i) => $"#{i+2000} = {n}")) {
+            Console.WriteLine(ludic);
+        }
+        Console.WriteLine();
+
+        Console.WriteLine("Triplets below 250:");
+        var queue = new Queue<int>(5);
+        foreach (int x in LudicNumbers(255)) {
+            if (queue.Count == 5) queue.Dequeue();
+            queue.Enqueue(x);
+            if (x - 6 < 250 && queue.Contains(x - 6) && queue.Contains(x - 4)) {
+                Console.WriteLine($"{x-6}, {x-4}, {x}");
+            }
+        }
+    }
+
+    public static IEnumerable<int> LudicNumbers(int limit) {
+        yield return 1;
+        //Like a linked list, but with value types.
+        //Create 2 extra entries at the start to avoid ugly index calculations
+        //and another at the end to avoid checking for index-out-of-bounds.
+        Entry[] values = Enumerable.Range(0, limit + 1).Select(n => new Entry(n)).ToArray();
+        for (int i = 2; i < limit; i = values[i].Next) {
+            yield return values[i].N;
+            int start = i;
+            while (start < limit) {
+                Unlink(values, start);
+                for (int step = 0; step < i && start < limit; step++)
+                    start = values[start].Next;
+            }
+        }
+    }
+
+    static void Unlink(Entry[] values, int index) {
+        values[values[index].Prev].Next = values[index].Next;
+        values[values[index].Next].Prev = values[index].Prev;
+    }
+
+}
+
+struct Entry
+{
+    public Entry(int n) : this() {
+        N = n;
+        Prev = n - 1;
+        Next = n + 1;
+    }
+
+    public int N { get; }
+    public int Prev { get; set; }
+    public int Next { get; set; }
+}