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Find maximum sum taking every Kth element in the array
• Last Updated : 08 Jun, 2021

Given an array arr[] of integers and an integer K, the task is to find the maximum sum taking every Kth element i.e. sum = arr[i] + arr[i + k] + arr[i + 2 * k] + arr[i + 3 * k] + ……. arr[i + q * k] starting with any i.
Examples:

Input: arr[] = {3, -5, 6, 3, 10}, K = 3
Output: 10
All possible sequence are:
3 + 3 = 6
-5 + 10 = 5
6 = 6
3 = 3
10 = 10
Input: arr[] = {3, 6, 4, 7, 2}, K = 2
Output: 13

Naive Approach: The idea to solve this by using two nested loops and find the sum of every sequence starting from index i and sum every Kth element up to n, and find the maximum from all of these. The time complexity of this method will be O(N2)
Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach``#include ``using` `namespace` `std;` `// Function to return the maximum sum for``// every possible sequence such that``// a[i] + a[i+k] + a[i+2k] + ... + a[i+qk]``// is maximized``int` `maxSum(``int` `arr[], ``int` `n, ``int` `K)``{` `    ``// Initialize the maximum with``    ``// the smallest value``    ``int` `maximum = INT_MIN;` `    ``// Find maximum from all sequences``    ``for` `(``int` `i = 0; i < n; i++) {` `        ``int` `sumk = 0;` `        ``// Sum of the sequence``        ``// starting from index i``        ``for` `(``int` `j = i; j < n; j += K)``            ``sumk = sumk + arr[j];` `        ``// Update maximum``        ``maximum = max(maximum, sumk);``    ``}` `    ``return` `maximum;``}` `// Driver code``int` `main()``{``    ``int` `arr[] = { 3, 6, 4, 7, 2 };``    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr);``    ``int` `K = 2;` `    ``cout << maxSum(arr, n, K);` `    ``return` `(0);``}`

## Java

 `// Java implementation of the approach``class` `GFG``{``    ` `// Function to return the maximum sum for``// every possible sequence such that``// a[i] + a[i+k] + a[i+2k] + ... + a[i+qk]``// is maximized``static` `int` `maxSum(``int` `arr[], ``int` `n, ``int` `K)``{` `    ``// Initialize the maximum with``    ``// the smallest value``    ``int` `maximum = Integer.MIN_VALUE;` `    ``// Find maximum from all sequences``    ``for` `(``int` `i = ``0``; i < n; i++)``    ``{` `        ``int` `sumk = ``0``;` `        ``// Sum of the sequence``        ``// starting from index i``        ``for` `(``int` `j = i; j < n; j += K)``            ``sumk = sumk + arr[j];` `        ``// Update maximum``        ``maximum = Math.max(maximum, sumk);``    ``}` `    ``return` `maximum;``}` `// Driver code``public` `static` `void` `main(String[] args)``{``    ``int` `arr[] = { ``3``, ``6``, ``4``, ``7``, ``2` `};``    ``int` `n = arr.length;``    ``int` `K = ``2``;` `    ``System.out.println(maxSum(arr, n, K));``}``}` `// This code is contributed by Code_Mech`

## Python3

 `# Python 3 implementation of the approach``import` `sys` `# Function to return the maximum sum for``# every possible sequence such that``# a[i] + a[i+k] + a[i+2k] + ... + a[i+qk]``# is maximized``def` `maxSum(arr, n, K):``    ` `    ``# Initialize the maximum with``    ``# the smallest value``    ``maximum ``=` `-``sys.maxsize ``-` `1` `    ``# Find maximum from all sequences``    ``for` `i ``in` `range``(n):``        ``sumk ``=` `0` `        ``# Sum of the sequence``        ``# starting from index i``        ``for` `j ``in` `range``(i, n, K):``            ``sumk ``=` `sumk ``+` `arr[j]` `        ``# Update maximum``        ``maximum ``=` `max``(maximum, sumk)` `    ``return` `maximum` `# Driver code``if` `__name__ ``=``=` `'__main__'``:``    ``arr ``=` `[``3``, ``6``, ``4``, ``7``, ``2``]``    ``n ``=` `len``(arr)``    ``K ``=` `2``    ``print``(maxSum(arr, n, K))``    ` `# This code is contributed by``# Surendra_Gangwar`

## C#

 `// C# implementation of the approach``using` `System;` `class` `GFG``{``    ` `// Function to return the maximum sum for``// every possible sequence such that``// a[i] + a[i+k] + a[i+2k] + ... + a[i+qk]``// is maximized``static` `int` `maxSum(``int` `[]arr, ``int` `n, ``int` `K)``{` `    ``// Initialize the maximum with``    ``// the smallest value``    ``int` `maximum = ``int``.MinValue;` `    ``// Find maximum from all sequences``    ``for` `(``int` `i = 0; i < n; i++)``    ``{` `        ``int` `sumk = 0;` `        ``// Sum of the sequence``        ``// starting from index i``        ``for` `(``int` `j = i; j < n; j += K)``            ``sumk = sumk + arr[j];` `        ``// Update maximum``        ``maximum = Math.Max(maximum, sumk);``    ``}` `    ``return` `maximum;``}` `// Driver code``public` `static` `void` `Main()``{``    ``int` `[]arr = { 3, 6, 4, 7, 2 };``    ``int` `n = arr.Length;``    ``int` `K = 2;` `    ``Console.WriteLine(maxSum(arr, n, K));``}``}` `// This code is contributed by Akanksha Rai`

## PHP

 ``

## Javascript

 ``
Output:

`13`

Efficient Approach: This problem can be solved by using the concept of Suffix Arrays, we iterate the array from right side and store the suffix sum for each (i+k)’th element (ie., i+k < n) , and find the maximum sum. The time complexity of this method will be O(N).
Below is the implementation of the above approach.

## C++

 `// C++ implementation of the approach``#include ``using` `namespace` `std;` `// Function to return the maximum sum for``// every possible sequence such that``// a[i] + a[i+k] + a[i+2k] + ... + a[i+qk]``// is maximized``int` `maxSum(``int` `arr[], ``int` `n, ``int` `K)``{` `    ``// Initialize the maximum with``    ``// the smallest value``    ``int` `maximum = INT_MIN;` `    ``// Initialize the sum array with zero``    ``int` `sum[n] = { 0 };` `    ``// Iterate from the right``    ``for` `(``int` `i = n - 1; i >= 0; i--) {` `        ``// Update the sum starting at``        ``// the current element``        ``if` `(i + K < n)``            ``sum[i] = sum[i + K] + arr[i];``        ``else``            ``sum[i] = arr[i];` `        ``// Update the maximum so far``        ``maximum = max(maximum, sum[i]);``    ``}` `    ``return` `maximum;``}` `// Driver code``int` `main()``{``    ``int` `arr[] = { 3, 6, 4, 7, 2 };``    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr);``    ``int` `K = 2;` `    ``cout << maxSum(arr, n, K);` `    ``return` `(0);``}`

## Java

 `// Java implementation of the approach``class` `GFG {` `    ``// Function to return the maximum sum for``    ``// every possible sequence such that``    ``// a[i] + a[i+k] + a[i+2k] + ... + a[i+qk]``    ``// is maximized``    ``static` `int` `maxSum(``int` `arr[], ``int` `n, ``int` `K)``    ``{` `        ``// Initialize the maximum with``        ``// the smallest value``        ``int` `maximum = Integer.MIN_VALUE;` `        ``// Initialize the sum array with zero``        ``int``[] sum = ``new` `int``[n];` `        ``// Iterate from the right``        ``for` `(``int` `i = n - ``1``; i >= ``0``; i--) {` `            ``// Update the sum starting at``            ``// the current element``            ``if` `(i + K < n)``                ``sum[i] = sum[i + K] + arr[i];``            ``else``                ``sum[i] = arr[i];` `            ``// Update the maximum so far``            ``maximum = Math.max(maximum, sum[i]);``        ``}` `        ``return` `maximum;``    ``}` `    ``// Driver code``    ``public` `static` `void` `main(String[] args)``    ``{``        ``int` `arr[] = { ``3``, ``6``, ``4``, ``7``, ``2` `};``        ``int` `n = arr.length;``        ``int` `K = ``2``;` `        ``System.out.print(maxSum(arr, n, K));``    ``}``}`

## Python

 `# Python implementation of the approach` `# Function to return the maximum sum for``# every possible sequence such that``# a[i] + a[i + k] + a[i + 2k] + ... + a[i + qk]``# is maximized``def` `maxSum(arr, n, K):``    ` `    ``# Initialize the maximum with``    ``# the smallest value``    ``maximum ``=` `-``2``*``*``32``;` `    ``# Initialize the sum array with zero``    ``sum` `=` `[``0``]``*``n` `    ``# Iterate from the right``    ``for` `i ``in` `range``(n``-``1``, ``-``1``, ``-``1``):``        ` `        ``# Update the sum starting at``        ``# the current element``        ``if``( i ``+` `K < n ):``            ``sum``[i] ``=` `sum``[i ``+` `K] ``+` `arr[i]``        ``else``:``            ``sum``[i] ``=` `arr[i];``    ` `        ``# Update the maximum so far``        ``maximum ``=` `max``( maximum, ``sum``[i] )``    ` `    ``return` `maximum;` `# Driver code``arr ``=` `[``3``, ``6``, ``4``, ``7``, ``2``]``n ``=` `len``(arr);``K ``=` `2``print``(maxSum(arr, n, K))`

## C#

 `// C# implementation of the approach``using` `System;``class` `GFG {` `    ``// Function to return the maximum sum for``    ``// every possible sequence such that``    ``// a[i] + a[i+k] + a[i+2k] + ... + a[i+qk]``    ``// is maximized``    ``static` `int` `maxSum(``int``[] arr, ``int` `n, ``int` `K)``    ``{` `        ``// Initialize the maximum with``        ``// the smallest value``        ``int` `maximum = ``int``.MinValue;` `        ``// Initialize the sum array with zero``        ``int``[] sum = ``new` `int``[n];` `        ``// Iterate from the right``        ``for` `(``int` `i = n - 1; i >= 0; i--) {` `            ``// Update the sum starting at``            ``// the current element``            ``if` `(i + K < n)``                ``sum[i] = sum[i + K] + arr[i];``            ``else``                ``sum[i] = arr[i];` `            ``// Update the maximum so far``            ``maximum = Math.Max(maximum, sum[i]);``        ``}` `        ``return` `maximum;``    ``}` `    ``// Driver code``    ``public` `static` `void` `Main()``    ``{``        ``int``[] arr = { 3, 6, 4, 7, 2 };``        ``int` `n = arr.Length;``        ``int` `K = 2;` `        ``Console.Write(maxSum(arr, n, K));``    ``}``}`

## PHP

 `= 0; ``\$i``--)``    ``{` `        ``// Update the sum starting at``        ``// the current element``        ``if` `(``\$i` `+ ``\$K` `< ``\$n``)``            ``\$sum``[``\$i``] = ``\$sum``[``\$i` `+ ``\$K``] + ``\$arr``[``\$i``];``        ``else``            ``\$sum``[``\$i``] = ``\$arr``[``\$i``];` `        ``// Update the maximum so far``        ``\$maximum` `= max(``\$maximum``, ``\$sum``[``\$i``]);``    ``}` `    ``return` `\$maximum``;``}` `// Driver code``{``    ``\$arr` `= ``array``(3, 6, 4, 7, 2 );``    ``\$n` `= sizeof(``\$arr``);``    ``\$K` `= 2;` `    ``echo``(maxSum(``\$arr``, ``\$n``, ``\$K``));``}` `// This code is contributed by Learner_`

## Javascript

 ``
Output:
`13`

Time Complexity: O(N) where N is the number of elements in array.

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