using System;using System.Net.Sockets;using System.Collections.Concurrent;using System.Threading;using System.Threading.Tasks;using System.Collections.Generic;
public class PScan{
 public static List<int> Scan(string host,int from,int to,int conc,int timeoutMs){
  var open=new ConcurrentBag<int>(); var sem=new SemaphoreSlim(conc); var tasks=new List<Task>();
  for(int p=from;p<=to;p++){
   int port=p; sem.Wait();
   tasks.Add(Task.Run(async ()=>{
    try{ using(var c=new TcpClient()){ var t=c.ConnectAsync(host,port); var done=await Task.WhenAny(t,Task.Delay(timeoutMs)); if(done==t&&c.Connected){ open.Add(port); } } }
    catch{}
    finally{ sem.Release(); }
   }));
  }
  Task.WaitAll(tasks.ToArray());
  var l=new List<int>(open); l.Sort(); return l;
 }
}