Learn Big O Notation - Simple way

What is Big O Notation?

Big O Notation used in computer science to measure the performance or complexity of an algorithm.

Below are the some examples for Big O Notation

O(1) - Order of 1

Describes an algorithm that will always execute in the same time or space irrespective of the input size. Example. Lets assume dataset length is 5. If dataset length is 5 or whatever below code will execute only one time i.e dataset[0].

function NullCheckForFirstElement(List dataset)

{

    return dataset[0] == null;

}

O(N) - Order of N

Describes an algorithm which always execute all the elements in the dataset. If dataset length is 5 then order of execution also 5. It matches direct proportion based on the dataset length.  For example

function ContainsValue(List<string> elements, string value)
{
foreach (var element in elements)
{
    if (element == value) return true;
}

return false;
}

O(N²)  - Order of N²

Describes an algorithm which always perform square of the N execution. Look at the below example. If elements size is 5 then for loop executes 5x5 = 25 times which means 5²

function checkDuplicates(List<string> elements)
{
     for (var i = 0; i < elements.Count; i++)
    {
       for (var j = 0; j < elements.Count; j++)
      {
         if (i == j) continue;

         if (elements[i] == elements[j]) return true;
      }
    }

return false;
}

O(2^N)

O(2N)

Describes an algorithm which executes total number of elements two times. For example

function showData(int arr[], int size)

{

     for(int i = 0; i < size; i++)

         System.out.print(arr[i]);

     for(int i = 0; i < size; i++)

         System.out.print(arr[i]);

}

This one is called O(2n) which we say O(N).