Stack.Contains() Method in C#

The Stack.Contains() method in C# is used to check whether a specific element exists in the Stack or not. It returns true if the element is found, otherwise false.

Syntax

The syntax for the Stack.Contains() method is as follows −

public virtual bool Contains(object obj);

Parameters

• obj − The object to be searched in the stack. It can be null.

Return Value

Returns a bool value −

• true − if the element is found in the Stack

• false − if the element is not found in the Stack

Using Contains() with String Elements

Example

using System;
using System.Collections;

public class Demo {
   public static void Main() {
      Stack stack = new Stack();
      stack.Push("Inspiron");
      stack.Push("Alienware");
      stack.Push("Projectors");
      stack.Push("Monitors");
      stack.Push("XPS");
      stack.Push("Laptop");
      stack.Push("Notebook");
      
      Console.WriteLine("Stack elements...");
      foreach(string val in stack) {
         Console.WriteLine(val);
      }
      
      Console.WriteLine("Count of elements = " + stack.Count);
      Console.WriteLine("Element 'Speakers' is in the stack? = " + stack.Contains("Speakers"));
      Console.WriteLine("Element 'Alienware' is in the stack? = " + stack.Contains("Alienware"));
   }
}

The output of the above code is −

Stack elements...
Notebook
Laptop
XPS
Monitors
Projectors
Alienware
Inspiron
Count of elements = 7
Element 'Speakers' is in the stack? = False
Element 'Alienware' is in the stack? = True

Using Contains() with Numeric Elements

Example

using System;
using System.Collections;

public class Demo {
   public static void Main() {
      Stack stack = new Stack();
      stack.Push(150);
      stack.Push(300);
      stack.Push(500);
      stack.Push(750);
      stack.Push(1000);
      stack.Push(1250);
      stack.Push(1500);
      stack.Push(2000);
      stack.Push(2500);
      
      Console.WriteLine("Stack elements...");
      foreach(int val in stack) {
         Console.WriteLine(val);
      }
      
      Console.WriteLine("Count of elements = " + stack.Count);
      Console.WriteLine("Element 750 is in the stack? = " + stack.Contains(750));
      Console.WriteLine("Element 5000 is in the stack? = " + stack.Contains(5000));
   }
}

The output of the above code is −

Stack elements...
2500
2000
1500
1250
1000
750
500
300
150
Count of elements = 9
Element 750 is in the stack? = True
Element 5000 is in the stack? = False

How It Works

The Contains() method performs a linear search through the Stack elements from top to bottom. It uses the Object.Equals() method to compare each element with the specified object. The search stops as soon as a match is found or all elements have been checked.

The time complexity is O(n) where n is the number of elements in the Stack, as it may need to examine every element in the worst case.

Conclusion

The Stack.Contains() method provides a convenient way to check if an element exists in a Stack collection. It returns a boolean value indicating whether the specified object is present, making it useful for validation and conditional operations in your applications.