C# | Check whether an element is contained in the ArrayList

ArrayList represents an ordered collection of an object that can be indexed individually. It is basically an alternative to an array. It also allows dynamic memory allocation, adding, searching and sorting items in the list. ArrayList.Contains(Object) method determines whether the element exists in ArrayList or not. Properties of ArrayList Class: 

• Elements can be added or removed from the Array List collection at any point in time.
• The ArrayList is not guaranteed to be sorted.
• The capacity of an ArrayList is the number of elements the ArrayList can hold.
• Elements in this collection can be accessed using an integer index. Indexes in this collection are zero-based.
• It also allows duplicate elements.
• Using multidimensional arrays as elements in an ArrayList collection is not supported.

Syntax:

public virtual bool Contains (object item);

Here, item is an Object to locate in the ArrayList. The value can be null. Return Value: This method will return True if the item found in the ArrayList otherwise it returns False. Note: This method performs a linear search, therefore, this method is an O(n) operation, where n is Count. Below are the programs to illustrate the ArrayList.Contains(Object) method: Example 1:

CSHARP

// C# code to check if an element is
// contained in ArrayList or not
using System;
using System.Collections;
using System.Collections.Generic;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating an ArrayList
        ArrayList myList = new ArrayList();

        // Adding elements to ArrayList
        myList.Add("A");
        myList.Add("B");
        myList.Add("C");
        myList.Add("D");
        myList.Add("E");
        myList.Add("F");
        myList.Add("G");
        myList.Add("H");

        // To check if the ArrayList Contains element "E"
        // If yes, then display it's index, else
        // display the message
        if (myList.Contains("E"))
            Console.WriteLine("Yes, exists at index " + myList.IndexOf("E"));
        else
            Console.WriteLine("No, doesn't exists");
    }
}

Output:

Yes, exists at index 4

Example 2 :

CSHARP

// C# code to check if an element is
// contained in ArrayList or not
using System;
using System.Collections;
using System.Collections.Generic;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating an ArrayList
        ArrayList myList = new ArrayList();

        // Adding elements to ArrayList
        myList.Add("5");
        myList.Add("7");
        myList.Add("9");
        myList.Add("11");
        myList.Add("12");
        myList.Add("16");
        myList.Add("20");
        myList.Add("25");

        // To check if the ArrayList Contains element "24"
        // If yes, then display it's index, else
        // display the message
        if (myList.Contains("24"))
            Console.WriteLine("Yes, exists at index " + myList.IndexOf("24"));
        else
            Console.WriteLine("No, doesn't exists");
    }
}

Output:

No, doesn't exists

Time complexity: O(n) since using Contains method

Auxiliary Space: O(n) where n is the size of the ArrayList

Reference: 

• https://docs.microsoft.com/en-us/dotnet/api/system.collections.arraylist.contains?view=netframework-4.7.2