Sum of even numbers at even position

Given an array of size n. The problem is to find the sum of numbers that are even and are at even index.

Examples:

Input :  arr[] = {5, 6, 12, 1, 18, 8}
Output : 30
Explanation: Here, n = 6 
Now here are index and numbers as: index->arr[index]
0->5, 1->6, 2->12, 3->1, 4->18, 5->8
so, number which are even and are at even indices 
are: 2->12, 4->18
sum = 12+18 = 30

Input  : arr[] = {3, 20, 17, 9, 2, 10, 
                        18, 13, 6, 18}
Output : 26
Explanation: Here, n = 10
Now here are index and numbers as: index->arr[index]
0->3, 1->20, 2->17, 3->9, 4->2, 5->10, 
6->18, 7->13, 8->6, 9->18 
So, number which are even and are at even indices are: 
4->2, 6->18, 8->6
sum = 2+18+6 = 26

Implementation:

C++

// C++ implementation to
// find sum of even numbers
// at even indices
#include <bits/stdc++.h>
using namespace std;

// Function to calculate sum
// of even numbers at even indices
int sum_even_and_even_index(
                int arr[], int n) {

    int i = 0, sum = 0;

    // calculating sum of even
    // number at even index
    for (i = 0; i < n; i+=2) {

        if (arr[i] % 2 == 0) {

            sum += arr[i];
        }
    }

    // required sum
    return sum;
}

// Driver program to test above
int main() {
    int arr[] = {5, 6, 12, 1, 18, 8};
    int n = sizeof(arr) / sizeof(arr[0]);
    cout << "Sum of even numbers at even indices is "
         << sum_even_and_even_index(arr, n);

    return 0;
}

Java

// Java implementation to find sum of
// even numbers at even indices

import java.io.*;

class GFG {

    // Function to calculate sum
    // of even numbers at even indices
    static int sum_even_and_even_index(
                       int arr[], int n)
    {

        int i = 0, sum = 0;

        // calculating sum of even
        // number at even index
        for (i = 0; i < n; i+=2) {

            if (arr[i] % 2 == 0) {
                sum += arr[i];
            }
        }

        // required sum
        return sum;
    }

    // Driver program to test above
    public static void main (String[] args) {

        int arr[] = {5, 6, 12, 1, 18, 8};
        int n = arr.length;
        System.out.println("Sum of even numbers"
                      + " at even indices is " +
             + sum_even_and_even_index(arr, n));
    }
}

// This code is contributed by vt_m.

Python3

# python 3 implementation to
# find sum of even numbers
# at even indices

# Function to calculate sum
# of even numbers at even indices
def sum_even_and_even_index(arr,n):

    i = 0
    sum = 0

# calculating sum of even
# number at even index
    for i in range(0,n,2):
        if (arr[i] % 2 == 0) :
            sum += arr[i]

    # required sum
    return sum


# Driver program to test above
arr = [5, 6, 12, 1, 18, 8]
n = len(arr)
print("Sum of even numbers at",
             "even indices is",
   sum_even_and_even_index(arr, n))

# This code is contributed by Sam007

C#

// C# implementation to find sum of
// even numbers at even indices

using System;

class GFG {

    // Function to calculate sum
    // of even numbers at even indices
    static int sum_even_and_even_index(
                    int []arr, int n)
    {

        int i = 0, sum = 0;

        // calculating sum of even
        // number at even index
        for (i = 0; i < n; i+=2) {

            if (arr[i] % 2 == 0) {

                sum += arr[i];
            }
        }

        // required sum
        return sum;
    }

    // Driver program to test above
    public static void Main () {

        int []arr = {5, 6, 12, 1, 18, 8};
        int n = arr.Length;
        Console.WriteLine("Sum of even numbers"
                    + " at even indices is " +
            + sum_even_and_even_index(arr, n));
    }
}

//This code is contributed by vt_m.

PHP

<?php
// PHP implementation to
// find sum of even numbers
// at even indices

// Function to calculate sum
// of even numbers at even indices
function sum_even_and_even_index($arr, $n)
{

    $i = 0; $sum = 0;

    // calculating sum of even
    // number at even index
    for ($i = 0; $i < $n; $i=$i+2) {

        if ($arr[$i] % 2 == 0) {

            $sum += $arr[$i];
        }
    }

    // required sum
    return $sum;
}

// Driver Code
{
    $arr = array(5, 6, 12, 1, 18, 8);
    $n = sizeof($arr) / sizeof($arr[0]);
    echo "Sum of even numbers at ".
                 "even indices is ",
          sum_even_and_even_index($arr, $n);

    return 0;
}

// This code is contributed by nitin mittal.
?>

Javascript

<script>

// Javascript implementation to
// find sum of even numbers
// at even indices

// Function to calculate sum
// of even numbers at even indices
function sum_even_and_even_index(
                arr, n) {

    let i = 0, sum = 0;

    // calculating sum of even
    // number at even index
    for (i = 0; i < n; i += 2)
    {
        if (arr[i] % 2 == 0)
        {
            sum += arr[i];
        }
    }

    // required sum
    return sum;
}

// Driver code
    let arr = [5, 6, 12, 1, 18, 8];
    let n = arr.length;
    document.write("Sum of even numbers at even indices is "
        + sum_even_and_even_index(arr, n));

// This code is contributed by Mayank Tyagi

</script>

Output

Sum of even numbers at even indices is 30

Time Complexity: O(n)
Auxiliary Space: O(1) 

Approach: Using List comprehension in python and Bitwise & operator 

This method uses a list comprehension to create a new list of the even numbers at even indices in the array, and then we use the sum() function to calculate the sum of the numbers.

Python3

# python 3 implementation to
# find sum of even numbers
# at even indices


# Driver program to test above
arr = [5, 6, 12, 1, 18, 8]
n=len(arr)
#using list comprehension to find even values at even indices
even_sum = sum([arr[i] for i in range(0,n,2) if arr[i] & 1 != 1])
#printing output
print("Sum of even numbers at",
             "even indices is",
   even_sum)
# This code is contributed by tvsk

Output

Sum of even numbers at even indices is 30

Time Complexity: O(n)
Auxiliary Space: O(1)