Check if a HashSet and a specified collection share common element in C#

To check if a HashSet and a specified collection share a common element, we use the Overlaps() method in C#. This method returns true if the HashSet shares at least one element with the specified collection, and false otherwise.

Syntax

Following is the syntax for the Overlaps() method −

public bool Overlaps(IEnumerable<T> other)

Parameters

• other − The collection to compare with the current HashSet.

Return Value

Returns true if the HashSet and the specified collection share at least one common element; otherwise, false.

Using Overlaps() with Integer HashSets

The following example demonstrates checking for common elements between two integer HashSets −

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main(){
      HashSet<int> set1 = new HashSet<int>();
      set1.Add(25);
      set1.Add(50);
      set1.Add(75);
      set1.Add(100);
      set1.Add(125);
      set1.Add(150);
      Console.WriteLine("Elements in HashSet1");
      foreach(int val in set1){
         Console.WriteLine(val);
      }
      
      HashSet<int> set2 = new HashSet<int>();
      set2.Add(30);
      set2.Add(60);
      set2.Add(100);
      set2.Add(150);
      set2.Add(200);
      set2.Add(250);
      Console.WriteLine("Elements in HashSet2");
      foreach(int val in set2){
         Console.WriteLine(val);
      }
      Console.WriteLine("Do they share common elements? " + set1.Overlaps(set2));
   }
}

The output of the above code is −

Elements in HashSet1
25
50
75
100
125
150
Elements in HashSet2
30
60
100
150
200
250
Do they share common elements? True

Using Overlaps() with String HashSets

The following example shows how to check for overlapping elements in string collections −

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main(){
      HashSet<String> set1 = new HashSet<String>();
      set1.Add("Nathan");
      set1.Add("Tim");
      set1.Add("Tom");
      set1.Add("Jack");
      set1.Add("Steve");
      set1.Add("David");
      Console.WriteLine("Elements in HashSet1");
      foreach(string val in set1){
         Console.WriteLine(val);
      }
      
      HashSet<String> set2 = new HashSet<String>();
      set2.Add("Tom");
      set2.Add("Jack");
      set2.Add("Kevin");
      Console.WriteLine("Elements in HashSet2");
      foreach(string val in set2){
         Console.WriteLine(val);
      }
      Console.WriteLine("Do they share common elements? " + set1.Overlaps(set2));
   }
}

The output of the above code is −

Elements in HashSet1
Nathan
Tim
Tom
Jack
Steve
David
Elements in HashSet2
Tom
Jack
Kevin
Do they share common elements? True

Using Overlaps() with Arrays and Lists

The Overlaps() method works with any IEnumerable<T> collection, not just other HashSets −

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main(){
      HashSet<int> hashSet = new HashSet<int>{10, 20, 30, 40};
      
      int[] array = {5, 15, 25, 30};
      List<int> list = new List<int>{1, 2, 3, 4};
      
      Console.WriteLine("HashSet overlaps with array: " + hashSet.Overlaps(array));
      Console.WriteLine("HashSet overlaps with list: " + hashSet.Overlaps(list));
   }
}

The output of the above code is −

HashSet overlaps with array: True
HashSet overlaps with list: False

Conclusion

The Overlaps() method provides an efficient way to check if a HashSet shares any common elements with another collection. It works with any IEnumerable<T> collection and returns true if at least one element is found in both collections.