Queue.Contains() Method in C#

The Queue.Contains() method in C# is used to determine whether a specific element exists in the Queue. It returns true if the element is found, otherwise false. This method performs a linear search through the queue elements.

Syntax

Following is the syntax for the Queue<T>.Contains() method −

public bool Contains(T item);

Parameters

• item − The object to locate in the Queue. The value can be null for reference types.

Return Value

Returns true if the item is found in the Queue; otherwise, false.

Using Contains() with String Queue

Example

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main() {
      Queue<string> queue = new Queue<string>();
      queue.Enqueue("Gary");
      queue.Enqueue("Jack");
      queue.Enqueue("Ryan");
      queue.Enqueue("Kevin");
      queue.Enqueue("Mark");
      
      Console.WriteLine("Queue elements: " + string.Join(", ", queue));
      Console.WriteLine("Count of elements = " + queue.Count);
      Console.WriteLine("Does the queue contain 'Jack'? = " + queue.Contains("Jack"));
      Console.WriteLine("Does the queue contain 'Alice'? = " + queue.Contains("Alice"));
      
      // Search is case-sensitive
      Console.WriteLine("Does the queue contain 'jack'? = " + queue.Contains("jack"));
   }
}

The output of the above code is −

Queue elements: Gary, Jack, Ryan, Kevin, Mark
Count of elements = 5
Does the queue contain 'Jack'? = True
Does the queue contain 'Alice'? = False
Does the queue contain 'jack'? = False

Using Contains() with Integer Queue

Example

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main() {
      Queue<int> queue = new Queue<int>();
      queue.Enqueue(100);
      queue.Enqueue(200);
      queue.Enqueue(300);
      queue.Enqueue(400);
      
      Console.WriteLine("Queue elements: " + string.Join(", ", queue));
      Console.WriteLine("Count of elements = " + queue.Count);
      Console.WriteLine("Does the queue contain 300? = " + queue.Contains(300));
      Console.WriteLine("Does the queue contain 500? = " + queue.Contains(500));
      
      // Remove elements and check again
      queue.Dequeue(); // Remove 100
      Console.WriteLine("After dequeue, contains 100? = " + queue.Contains(100));
   }
}

The output of the above code is −

Queue elements: 100, 200, 300, 400
Count of elements = 4
Does the queue contain 300? = True
Does the queue contain 500? = False
After dequeue, contains 100? = False

Key Points

• The Contains() method uses the default equality comparer for the type to determine equality.

• For reference types, it can accept null as a valid search parameter.

• The search is case-sensitive for string comparisons.

• Time complexity is O(n) as it performs a linear search through all elements.

Conclusion

The Queue.Contains() method provides a simple way to check if an element exists in a queue. It performs a linear search and returns a boolean value indicating whether the specified element is found in the queue collection.