Ludic numbers: Difference between revisions
Added C#
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Triples below 250: (1 3 7) (5 7 11) (11 13 17) (23 25 29) (41 43 47) (173 175 179) (221 223 227) (233 235 239)
</pre>
=={{header|C sharp}}==
<lang csharp>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; }
}</lang>
{{out}}
<pre>
First 25 ludic numbers:
1, 2, 3, 5, 7, 11, 13, 17, 23, 25, 29, 37, 41, 43, 47, 53, 61, 67, 71, 77, 83, 89, 91, 97, 107
There are 142 ludic numbers below 1000
#2000 = 21475
#2001 = 21481
#2002 = 21487
#2003 = 21493
#2004 = 21503
#2005 = 21511
Triplets below 250:
1, 3, 7
5, 7, 11
11, 13, 17
23, 25, 29
41, 43, 47
173, 175, 179
221, 223, 227
233, 235, 239</pre>
=={{header|C++}}==
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