# Maximum possible array sum after performing the given operation

Given an array arr[] of size N, the task is to find the maximum sum of the elements of the array after applying the given operation any number of times. In a single operation, choose an index 1 ≤ i < N and multiply both arr[i] and arr[i – 1] by -1.

Examples:

Input: arr[] = {-10, 5, -4}
Output: 19
Perform the operation for i = 1 and
the array becomes {10, -5, -4}
Perform the operation for i = 2 and
the array becomes {10, 5, 4}
10 + 5 + 4 = 19

Input: arr[] = {10, -4, -8, -11, 3}
Output: 30

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach: This problem can be solved using dynamic programming. Since it is useless to choose and flip the same arr[i], we will consider flipping at most once for each element of the array in order from the left. Let dp[i] represents the maximum possible sum up to the ith index without flipping the ith index. dp[i] represents the maximum possible sum up to the ith index with flipping the ith index. So, dp(n, 0) is our required answer.

Base conditions:

1. dp = 0
2. dp = INT_MIN

Recurrence relation:

1. dp[i + 1] = max(dp[i] + arr[i], dp[i] – arr[i])
2. dp[i + 1] = max(dp[i] – arr[i], dp[i] + arr[i])

Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach ` `#include ` `using` `namespace` `std; ` ` `  `// Function to return the maximum possible ` `// sum after performing the given operation ` `int` `max_sum(``int` `a[], ``int` `n) ` `{ ` `    ``// Dp vector to store the answer ` `    ``vector > dp(n + 1, ` `                            ``vector<``int``>(2, 0)); ` ` `  `    ``// Base value ` `    ``dp = 0, dp = -999999; ` ` `  `    ``for` `(``int` `i = 0; i <= n - 1; i++) { ` `        ``dp[i + 1] = max(dp[i] + a[i], ` `                           ``dp[i] - a[i]); ` `        ``dp[i + 1] = max(dp[i] - a[i], ` `                           ``dp[i] + a[i]); ` `    ``} ` ` `  `    ``// Return the maximum sum ` `    ``return` `dp[n]; ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``int` `a[] = { -10, 5, -4 }; ` `    ``int` `n = ``sizeof``(a) / ``sizeof``(a); ` ` `  `    ``cout << max_sum(a, n); ` ` `  `    ``return` `0; ` `} `

## Java

 `// Java implementation of the approach ` `class` `GFG  ` `{ ` ` `  `// Function to return the maximum possible ` `// sum after performing the given operation ` `static` `int` `max_sum(``int` `a[], ``int` `n) ` `{ ` `    ``// Dp vector to store the answer ` `    ``int` `[][]dp = ``new` `int``[n + ``1``][``2``]; ` `                         `  `    ``// Base value ` `    ``dp[``0``][``0``] = ``0``; dp[``0``][``1``] = -``999999``; ` ` `  `    ``for` `(``int` `i = ``0``; i <= n - ``1``; i++)  ` `    ``{ ` `        ``dp[i + ``1``][``0``] = Math.max(dp[i][``0``] + a[i], ` `                                ``dp[i][``1``] - a[i]); ` `        ``dp[i + ``1``][``1``] = Math.max(dp[i][``0``] - a[i], ` `                                ``dp[i][``1``] + a[i]); ` `    ``} ` ` `  `    ``// Return the maximum sum ` `    ``return` `dp[n][``0``]; ` `} ` ` `  `// Driver code ` `public` `static` `void` `main(String[] args)  ` `{ ` `    ``int` `a[] = { -``10``, ``5``, -``4` `}; ` `    ``int` `n = a.length; ` ` `  `    ``System.out.println(max_sum(a, n)); ` `} ` `} ` ` `  `// This code is contributed by 29AjayKumar `

## Python3

 `# Python implementation of the approach ` ` `  `# Function to return the maximum possible ` `# sum after performing the given operation ` `def` `max_sum(a, n): ` `    ``# Dp vector to store the answer ` `    ``dp ``=` `[[``0` `for` `i ``in` `range``(``2``)] ``for` `j ``in` `range``(n``+``1``)] ` `                         `  `    ``# Base value ` `    ``dp[``0``][``0``] ``=` `0``; dp[``0``][``1``] ``=` `-``999999``; ` ` `  `    ``for` `i ``in` `range``(``0``, n):  ` `        ``dp[i ``+` `1``][``0``] ``=` `max``(dp[i][``0``] ``+` `a[i], ` `                                ``dp[i][``1``] ``-` `a[i]); ` `        ``dp[i ``+` `1``][``1``] ``=` `max``(dp[i][``0``] ``-` `a[i], ` `                                ``dp[i][``1``] ``+` `a[i]); ` ` `  `    ``# Return the maximum sum ` `    ``return` `dp[n][``0``]; ` ` `  `# Driver code ` `if` `__name__ ``=``=` `'__main__'``: ` `    ``a ``=` `[``-``10``, ``5``, ``-``4` `]; ` `    ``n ``=` `len``(a); ` ` `  `    ``print``(max_sum(a, n)); ` `     `  `# This code is contributed by 29AjayKumar `

## C#

 `// C# implementation of the approach ` `using` `System; ` `     `  `class` `GFG  ` `{ ` ` `  `// Function to return the maximum possible ` `// sum after performing the given operation ` `static` `int` `max_sum(``int` `[]a, ``int` `n) ` `{ ` `    ``// Dp vector to store the answer ` `    ``int` `[,]dp = ``new` `int``[n + 1, 2]; ` `                         `  `    ``// Base value ` `    ``dp[0, 0] = 0; dp[0, 1] = -999999; ` ` `  `    ``for` `(``int` `i = 0; i <= n - 1; i++)  ` `    ``{ ` `        ``dp[i + 1, 0] = Math.Max(dp[i, 0] + a[i], ` `                                ``dp[i, 1] - a[i]); ` `        ``dp[i + 1, 1] = Math.Max(dp[i, 0] - a[i], ` `                                ``dp[i, 1] + a[i]); ` `    ``} ` ` `  `    ``// Return the maximum sum ` `    ``return` `dp[n, 0]; ` `} ` ` `  `// Driver code ` `public` `static` `void` `Main(String[] args)  ` `{ ` `    ``int` `[]a = { -10, 5, -4 }; ` `    ``int` `n = a.Length; ` ` `  `    ``Console.WriteLine(max_sum(a, n)); ` `} ` `} ` ` `  `// This code is contributed by PrinciRaj1992 `

Output:

```19
```

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