Given a list of numbers and a number k, return whether any two numbers from the list add up to k, C#

Language: Layout:

using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Text.RegularExpressions;

namespace Rextester {

public class Program {

public static void Main(string[] args) { 
    int[] array1 = new int[] { 7,7,10,4,1,13}; 
    int k = 20;
    
var dup = array1.GroupBy(x => x)
              .Where(g => g.Count() > 1)
              .Select(y => y.Key)
              .ToList();
    
List < int > l = new List < int > (); 
    foreach(var item in array1) {
     
    if (array1.Contains(k - item))
    {
        if((k - item)!=item)
        if (!l.Contains(item)) {
        Console.WriteLine(item.ToString() + "+" + (k - item).ToString()+"="+k);
        l.Add((k - item));
      }
        if(dup.Contains(item) && (k - item)==item)
        if (!l.Contains(item)) {
        Console.WriteLine(item.ToString() + "+" + (k - item).ToString()+"="+k);
        l.Add((k - item));
      }
    }    
    } 
    if(l.Count()<1)
        {
         Console.WriteLine("No additives found");
        } 
    } 
} 
}

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Compilation time: 2.15 sec, absolute running time: 0.46 sec, cpu time: 0.24 sec, memory peak: 39 Mb, absolute service time: 2,69 sec

Given a list of numbers and a number k, return whether any two numbers...