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# Remove k corner elements to maximize remaining sum

• Difficulty Level : Basic
• Last Updated : 31 Aug, 2021

Given an array, the task is to remove total k elements from corners to maximize the sum of remaining elements. For example, if we k = 5 and if we remove 2 elements from the left corner, then we need to remove 3 elements from the right corner.
Examples:

Input : arr = [11, 49, 100, 20, 86, 29, 72], k = 4
Output : 206
Explanation :: We remove 29 and 72 from right corner. We also remove 11 and 49 from left corner to get the maximum sum as 206 for remaining elements.

Input : arr[] = [1, 2, 3, 4, 5, 6, 1], k = 3
Output : 18
Explanation :: We remove two elements from left corner (1 and 2) and one element from right corner (1).

Naive Approach :
1) Initialize result as negative infinity.
2) Compute total sum.
3) Run a loop for x = 1 to k
…..Remove ‘x’ elements from left side and k – i elements from right side.
…..If the remaining elements have sum more than the result, update the result.

Time Complexity: O(n * k)
Efficient Approach (Using Window Sliding Technique)
1) Find the sum of first n-k elements and initialize this as a current sum and also initialize this as result.
2) Run a loop for i = n-k to n-1
….curr_sum = curr_sum – arr[i – n + k] + arr[i]
….res = max(res, curr_sum)
In step 2, we mainly run sliding window. We remove an element from left side and add an element from right side.

Below is the c++ implementation of the above problem statement.

## C++

 `#include ``using` `namespace` `std;``int` `calculate(``int` `arr[], ``int` `n, ``int` `k)``{``    ``// Calculate the sum of all elements``    ``// excluding the last k elements..``    ``int` `curr_sum = 0;``    ``for` `(``int` `i = 0; i < n - k; i++)``        ``curr_sum += arr[i];` `    ``// now here its time to use sliding window``    ``// concept, remove the first element from``    ``// the current window and add the new element``    ``// in it in order to get the sum of all n-k size``    ``// of elements in arr.``    ``// Calculate the minimum sum of elements of``    ``// size n-k and stored it into the result``    ``int` `res = curr_sum;``    ``for` `(``int` `i = n - k; i < n; i++) {``        ``curr_sum = curr_sum - arr[i - n + k] + arr[i];``        ``res = max(res, curr_sum);``    ``}` `    ``// Now return result (sum of remaining n-k elements)``    ``return` `res;``}` `// main function``int` `main()``{``    ``int` `arr[] = { 11, 49, 100, 20, 86, 29, 72 };``    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr);``    ``int` `k = 4;``    ``cout << ``"Maximum sum of remaining elements "``         ``<< calculate(arr, n, k) << ``"\n"``;``    ``return` `0;``}`

## Java

 `// Java program for the``// above approach``import` `java.util.*;``class` `GFG{` `static` `int` `calculate(``int``[] arr,``                     ``int` `n, ``int` `k)``{``  ``// Calculate the total``  ``// sum of all elements``  ``// present in the array..``  ``int` `total_sum = ``0``;``  ` `  ``for` `(``int` `i = ``0``; i < n; i++)``    ``total_sum += arr[i];` `  ``// Now calculate the sum``  ``// of all elements excluding``  ``// the last k elements..``  ``int` `curr_sum = ``0``;``  ` `  ``for` `(``int` `i = ``0``; i < n - k; i++)``    ``curr_sum += arr[i];` `  ``// Now here its time to use``  ``// sliding window concept,``  ``// remove the first element``  ``// from the current window``  ``// and add the new element``  ``// in it in order to get``  ``// the sum of all n-k size``  ``// of elements in arr.``  ``// Calculate the minimum``  ``// sum of elements of``  ``// size n-k and stored it``  ``// into the result``  ``int` `res = curr_sum;``  ` `  ``for` `(``int` `i = n - k; i < n; i++)``  ``{``    ``curr_sum = curr_sum -``               ``arr[i - n + k] +``               ``arr[i];``    ``res = Math.max(res, curr_sum);``  ``}` `  ``// Now return result (sum of``  ``// remaining n-k elements)``  ``return` `res;``}` `// Driver code``public` `static` `void` `main(String[] args)``{``  ``int``[] arr = {``11``, ``49``, ``100``,``               ``20``, ``86``, ``29``, ``72``};``  ``int` `n = arr.length;``  ``int` `k = ``4``;``  ``System.out.print(``"Maximum sum of remaining "` `+``                   ``"elements "` `+``                    ``calculate(arr, n, k) + ``"\n"``);``}``}` `// This code is contributed by Chitranayal`

## Python3

 `def` `calculate(arr, n, k):``    ` `    ``# calculate the total sum of all elements``    ``# present in the array..``    ``total_sum ``=` `0``    ``for` `i ``in` `arr:``        ``total_sum ``+``=` `i` `    ``# now calculate the sum of all elements``    ``# excluding the last k elements..``    ``curr_sum ``=` `0``    ``for` `i ``in` `range``(n ``-` `k):``        ``curr_sum ``+``=` `arr[i]` `    ``# now here its time to use sliding window``    ``# concept, remove the first element from``    ``# the current window and add the new element``    ``# in it in order to get the sum of all n-k size``    ``# of elements in arr.``    ``# Calculate the minimum sum of elements of``    ``# size n-k and stored it into the result``    ``res ``=` `curr_sum``    ``for` `i ``in` `range``(n ``-` `k, n):``        ``curr_sum ``=` `curr_sum ``-` `arr[i ``-` `n ``+` `k] ``+` `arr[i]``        ``res ``=` `max``(res, curr_sum)` `    ``# Now return result (sum of remaining n-k elements)``    ``return` `res` `# main function``if` `__name__ ``=``=` `'__main__'``:``    ``arr``=``[``11``, ``49``, ``100``, ``20``, ``86``, ``29``, ``72``]``    ``n ``=` `len``(arr)``    ``k ``=` `4``    ``print``(``"Maximum sum of remaining elements "``,calculate(arr, n, k))` `# This code is contributed by mohit kumar 29   `

## C#

 `using` `System;``using` `System.Collections;``using` `System.Collections.Generic;` `class` `GFG{``  ` `static` `int` `calculate(``int` `[]arr, ``int` `n, ``int` `k)``{``    ` `    ``// Calculate the total sum of all elements``    ``// present in the array..``    ``int` `total_sum = 0;``    ``for``(``int` `i = 0; i < n; i++)``        ``total_sum += arr[i];`` ` `    ``// Now calculate the sum of all elements``    ``// excluding the last k elements..``    ``int` `curr_sum = 0;``    ``for``(``int` `i = 0; i < n - k; i++)``        ``curr_sum += arr[i];`` ` `    ``// Now here its time to use sliding window``    ``// concept, remove the first element from``    ``// the current window and add the new element``    ``// in it in order to get the sum of all n-k size``    ``// of elements in arr.``    ``// Calculate the minimum sum of elements of``    ``// size n-k and stored it into the result``    ``int` `res = curr_sum;``    ``for``(``int` `i = n - k; i < n; i++)``    ``{``        ``curr_sum = curr_sum -``                  ``arr[i - n + k] + arr[i];``        ``res = Math.Max(res, curr_sum);``    ``}`` ` `    ``// Now return result (sum of``    ``// remaining n-k elements)``    ``return` `res;``}` `// Driver code``public` `static` `void` `Main(``string``[] args)``{``    ``int` `[]arr = { 11, 49, 100, 20, 86, 29, 72 };``    ``int` `n = arr.Length;``    ``int` `k = 4;``    ` `    ``Console.Write(``"Maximum sum of remaining "` `+``                  ``"elements "` `+``                  ``calculate(arr, n, k) + ``"\n"``);``}``}` `// This code is contributed by rutvik_56`

## Javascript

 ``
Output:
`Maximum sum of remaining elements 206`

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

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