# Minimum sum of product of two arrays

Find the minimum sum of Products of two arrays of the same size, given that k modifications are allowed on the first array. In each modification, one array element of the first array can either be increased or decreased by 2.

Examples:

a[] = {1, 2, -3} b[] = {-2, 3, -5} k = 5Input :-31Output :Here n = 3 and k = 5. So, we modified a[2], which is -3 and increased it by 10 (as 5 modifications are allowed). Final sum will be : (1 * -2) + (2 * 3) + (7 * -5) -2 + 6 - 35 -31 (which is the minimum sum of the array with given conditions)Explanation:a[] = {2, 3, 4, 5, 4} b[] = {3, 4, 2, 3, 2} k = 3Input :25Output :Here, total numbers are 5 and total modifications allowed are 3. So, modify a[1], which is 3 and decreased it by 6 (as 3 modifications are allowed). Final sum will be : (2 * 3) + (-3 * 4) + (4 * 2) + (5 * 3) + (4 * 2) 6 – 12 + 8 + 15 + 8 25 (which is the minimum sum of the array with given conditions)Explanation:

Since we need to minimize the product sum, we find the maximum product and reduce it. By taking some examples, we observe that making 2*k changes to only one element is enough to get the minimum sum. We will further see why this works but first, let us try to understand the intuition behind doing an increase or decrease of 2*k on any element.

If you want to make the sum of all the products as minimum as possible then thinking greedily we will try to minimize the product at every step possible.

a[] = {1, 2, -3}

b[] = {-2, 3, -5}

At index = 0, the original product is (1*-2) = -2 If we want to decrease it further we would try to increase the value of a[0] in order to increase the -ve magnitude

At index = 1, the original product is (2*3) = 6 here there is only one way to decrease the product which is by decreasing a[1] in order to bring the product to -ve or lesser +ve magnitude.

At index = 2, the original product is (-3*-5) = 15, to decrease the product we need to increase a[2] to make the product -ve

Based on the needs we either increase or decrease an element by 2

#### Why are we applying 2*k operations on a single element only?

The question might have come to your mind why are we applying 2*k operations (either reducing or increasing) on a single element only, why not apply +2 on some * ith index *and -4 on some

*and then -2 on some*

*jth index**to find out the minimum product sum. Wouldn’t there be a possibility that applying operations on different elements fetch us the optimal answer?*

*kth index*Let us try to understand the same with an example

a[] = {-4, -3, 2, 8, 9}

b[] = {7, -6, 4, 2, -3}

K = 3

Now if I apply 2*k operations on my 0th index of a then a[0] = a[0] – 2*k = -10 so the product = -10*7 = -70

Had it been applied in a different manner such as -2 on the * 0th index*, +2 on the

*, and -2 on the*

*1th index**then array*

*3th index***would be a[] ={-6, -1, 2, 6, 9} and the products at respective indices would be -42, 6, and 12 so our overall reduction = -24 which is less than the case when 2*k operations are being applied on a single element.**

**a**Just think in the way that if applying an operation on any element decreases your product then applying the rest of the operation on the same element would further decrease your product and eventually your sum and that’s the most optimal way.

**I would suggest you write down a few test cases of your own and try applying operations in different ways.**

Based on this observation, we consider every element as the element on which we apply all k operations and keep track of the element that reduces the result to a minimum.

## C++

`// CPP program to find minimum sum of product of two arrays` `// with k operations allowed on first array.` `#include <bits/stdc++.h>` `using` `namespace` `std;` `// Function to find the minimum product` `int` `minproduct(` `int` `a[], ` `int` `b[], ` `int` `n, ` `int` `k)` `{` ` ` `int` `diff = 0, res = 0;` ` ` `int` `temp;` ` ` `for` `(` `int` `i = 0; i < n; i++) {` ` ` `// Find product of current elements and update` ` ` `// result.` ` ` `int` `pro = a[i] * b[i];` ` ` `res = res + pro;` ` ` `// If both product and b[i] are negative, we must` ` ` `// increase value of a[i] to minimize result.` ` ` `if` `(pro < 0 && b[i] < 0)` ` ` `temp = (a[i] + 2 * k) * b[i];` ` ` `// If both product and a[i] are negative, we must` ` ` `// decrease value of a[i] to minimize result.` ` ` `else` `if` `(pro < 0 && a[i] < 0)` ` ` `temp = (a[i] - 2 * k) * b[i];` ` ` `// Similar to above two cases for positive product.` ` ` `else` `if` `(pro > 0 && a[i] < 0)` ` ` `temp = (a[i] + 2 * k) * b[i];` ` ` `else` `if` `(pro > 0 && a[i] > 0)` ` ` `temp = (a[i] - 2 * k) * b[i];` ` ` `// Check if current difference becomes higher than` ` ` `// the maximum difference so far.` ` ` `int` `d = ` `abs` `(pro - temp);` ` ` `if` `(d > diff)` ` ` `diff = d;` ` ` `}` ` ` `return` `res - diff;` `}` `// Driver function` `int` `main()` `{` ` ` `int` `a[] = { 2, 3, 4, 5, 4 };` ` ` `int` `b[] = { 3, 4, 2, 3, 2 };` ` ` `int` `n = 5, k = 3;` ` ` `cout << minproduct(a, b, n, k) << endl;` ` ` `return` `0;` `}` `// This code is contributed by Sania Kumari Gupta` |

## C

`// C program to find minimum sum of product` `// of two arrays with k operations allowed on` `// first array.` `#include <stdio.h>` `#include<stdlib.h>` `// Function to find the minimum product` `int` `minproduct(` `int` `a[], ` `int` `b[], ` `int` `n, ` `int` `k)` `{` ` ` `int` `diff = 0, res = 0;` ` ` `int` `temp;` ` ` `for` `(` `int` `i = 0; i < n; i++) {` ` ` `// Find product of current elements and update` ` ` `// result.` ` ` `int` `pro = a[i] * b[i];` ` ` `res = res + pro;` ` ` `// If both product and b[i] are negative, we must` ` ` `// increase value of a[i] to minimize result.` ` ` `if` `(pro < 0 && b[i] < 0)` ` ` `temp = (a[i] + 2 * k) * b[i];` ` ` `// If both product and a[i] are negative, we must` ` ` `// decrease value of a[i] to minimize result.` ` ` `else` `if` `(pro < 0 && a[i] < 0)` ` ` `temp = (a[i] - 2 * k) * b[i];` ` ` `// Similar to above two cases for positive product.` ` ` `else` `if` `(pro > 0 && a[i] < 0)` ` ` `temp = (a[i] + 2 * k) * b[i];` ` ` `else` `if` `(pro > 0 && a[i] > 0)` ` ` `temp = (a[i] - 2 * k) * b[i];` ` ` `// Check if current difference becomes higher than` ` ` `// the maximum difference so far.` ` ` `int` `d = ` `abs` `(pro - temp);` ` ` `if` `(d > diff)` ` ` `diff = d;` ` ` `}` ` ` `return` `res - diff;` `}` `// Driver function` `int` `main()` `{` ` ` `int` `a[] = { 2, 3, 4, 5, 4 };` ` ` `int` `b[] = { 3, 4, 2, 3, 2 };` ` ` `int` `n = 5, k = 3;` ` ` `printf` `(` `"%d "` `,minproduct(a, b, n, k));` ` ` `return` `0;` `}` `// This code is contributed by Sania Kumari Gupta` |

## Java

`// Java program to find minimum sum of product of two arrays` `// with k operations allowed on first array.` `import` `java.math.*;` `class` `GFG {` ` ` `// Function to find the minimum product` ` ` `static` `int` `minproduct(` `int` `a[], ` `int` `b[], ` `int` `n, ` `int` `k)` ` ` `{` ` ` `int` `diff = ` `0` `, res = ` `0` `;` ` ` `int` `temp = ` `0` `;` ` ` `for` `(` `int` `i = ` `0` `; i < n; i++) {` ` ` `// Find product of current elements and update` ` ` `// result.` ` ` `int` `pro = a[i] * b[i];` ` ` `res = res + pro;` ` ` `// If both product and b[i] are negative, we` ` ` `// must increase value of a[i] to minimize` ` ` `// result.` ` ` `if` `(pro < ` `0` `&& b[i] < ` `0` `)` ` ` `temp = (a[i] + ` `2` `* k) * b[i];` ` ` `// If both product and a[i] are negative, we` ` ` `// must decrease value of a[i] to minimize` ` ` `// result.` ` ` `else` `if` `(pro < ` `0` `&& a[i] < ` `0` `)` ` ` `temp = (a[i] - ` `2` `* k) * b[i];` ` ` `// Similar to above two cases for positive` ` ` `// product.` ` ` `else` `if` `(pro > ` `0` `&& a[i] < ` `0` `)` ` ` `temp = (a[i] + ` `2` `* k) * b[i];` ` ` `else` `if` `(pro > ` `0` `&& a[i] > ` `0` `)` ` ` `temp = (a[i] - ` `2` `* k) * b[i];` ` ` `// Check if current difference becomes higher` ` ` `// than the maximum difference so far.` ` ` `int` `d = Math.abs(pro - temp);` ` ` `if` `(d > diff)` ` ` `diff = d;` ` ` `}` ` ` `return` `res - diff;` ` ` `}` ` ` `// Driver function` ` ` `public` `static` `void` `main(String[] args)` ` ` `{` ` ` `int` `a[] = { ` `2` `, ` `3` `, ` `4` `, ` `5` `, ` `4` `};` ` ` `int` `b[] = { ` `3` `, ` `4` `, ` `2` `, ` `3` `, ` `2` `};` ` ` `int` `n = ` `5` `, k = ` `3` `;` ` ` `System.out.println(minproduct(a, b, n, k));` ` ` `}` `}` `// This code is contributed by Sania Kumari Gupta` |

## Python3

`# Python program to find` `# minimum sum of product` `# of two arrays with k` `# operations allowed on` `# first array.` `# Function to find the minimum product` `def` `minproduct(a,b,n,k):` ` ` `diff ` `=` `0` ` ` `res ` `=` `0` ` ` `for` `i ` `in` `range` `(n):` ` ` `# Find product of current` ` ` `# elements and update result.` ` ` `pro ` `=` `a[i] ` `*` `b[i]` ` ` `res ` `=` `res ` `+` `pro` ` ` `# If both product and` ` ` `# b[i] are negative,` ` ` `# we must increase value` ` ` `# of a[i] to minimize result.` ` ` `if` `(pro < ` `0` `and` `b[i] < ` `0` `):` ` ` `temp ` `=` `(a[i] ` `+` `2` `*` `k) ` `*` `b[i]` ` ` `# If both product and` ` ` `# a[i] are negative,` ` ` `# we must decrease value` ` ` `# of a[i] to minimize result.` ` ` `elif` `(pro < ` `0` `and` `a[i] < ` `0` `):` ` ` `temp ` `=` `(a[i] ` `-` `2` `*` `k) ` `*` `b[i]` ` ` `# Similar to above two cases` ` ` `# for positive product.` ` ` `elif` `(pro > ` `0` `and` `a[i] < ` `0` `):` ` ` `temp ` `=` `(a[i] ` `+` `2` `*` `k) ` `*` `b[i]` ` ` `elif` `(pro > ` `0` `and` `a[i] > ` `0` `):` ` ` `temp ` `=` `(a[i] ` `-` `2` `*` `k) ` `*` `b[i]` ` ` `# Check if current difference` ` ` `# becomes higher` ` ` `# than the maximum difference so far.` ` ` `d ` `=` `abs` `(pro ` `-` `temp)` ` ` `if` `(d > diff):` ` ` `diff ` `=` `d ` ` ` `return` `res ` `-` `diff` `# Driver function` `a ` `=` `[ ` `2` `, ` `3` `, ` `4` `, ` `5` `, ` `4` `]` `b ` `=` `[ ` `3` `, ` `4` `, ` `2` `, ` `3` `, ` `2` `]` `n ` `=` `5` `k ` `=` `3` `print` `(minproduct(a, b, n, k))` `# This code is contributed` `# by Azkia Anam.` |

## C#

`// C# program to find minimum sum` `// of product of two arrays with k` `// operations allowed on first array.` `using` `System;` `class` `GFG {` ` ` `// Function to find the minimum product` ` ` `static` `int` `minproduct(` `int` `[]a, ` `int` `[]b,` ` ` `int` `n, ` `int` `k)` ` ` `{` ` ` `int` `diff = 0, res = 0;` ` ` `int` `temp = 0;` ` ` `for` `(` `int` `i = 0; i < n; i++)` ` ` `{` ` ` ` ` `// Find product of current elements` ` ` `// and update result.` ` ` `int` `pro = a[i] * b[i];` ` ` `res = res + pro;` ` ` ` ` `// If both product and b[i] are` ` ` `// negative, we must increase value` ` ` `// of a[i] to minimize result.` ` ` `if` `(pro < 0 && b[i] < 0)` ` ` `temp = (a[i] + 2 * k) * b[i];` ` ` ` ` `// If both product and a[i] are` ` ` `// negative, we must decrease value` ` ` `// of a[i] to minimize result.` ` ` `else` `if` `(pro < 0 && a[i] < 0)` ` ` `temp = (a[i] - 2 * k) * b[i];` ` ` ` ` `// Similar to above two cases` ` ` `// for positive product.` ` ` `else` `if` `(pro > 0 && a[i] < 0)` ` ` `temp = (a[i] + 2 * k) * b[i];` ` ` `else` `if` `(pro > 0 && a[i] > 0)` ` ` `temp = (a[i] - 2 * k) * b[i];` ` ` ` ` `// Check if current difference` ` ` `// becomes higher than the maximum` ` ` `// difference so far.` ` ` `int` `d = Math.Abs(pro - temp);` ` ` `if` `(d > diff)` ` ` `diff = d;` ` ` `}` ` ` ` ` `return` `res - diff;` ` ` `}` ` ` ` ` `// Driver function` ` ` `public` `static` `void` `Main()` ` ` `{` ` ` `int` `[]a = { 2, 3, 4, 5, 4 };` ` ` `int` `[]b = { 3, 4, 2, 3, 2 };` ` ` `int` `n = 5, k = 3;` ` ` ` ` `Console.WriteLine(minproduct(a, b, n, k));` ` ` `}` `}` `// This code is contributed by vt_m.` |

## Javascript

`<script>` `// Javascript program to find minimum sum` `// of product of two arrays with k` `// operations allowed on first array.` `// Function to find the minimum product` `function` `minproduct(a, b, n, k)` `{` ` ` `let diff = 0, res = 0;` ` ` `let temp = 0;` ` ` `for` `(let i = 0; i < n; i++)` ` ` `{` ` ` ` ` `// Find product of current elements` ` ` `// and update result.` ` ` `let pro = a[i] * b[i];` ` ` `res = res + pro;` ` ` ` ` `// If both product and b[i] are` ` ` `// negative, we must increase value` ` ` `// of a[i] to minimize result.` ` ` `if` `(pro < 0 && b[i] < 0)` ` ` `temp = (a[i] + 2 * k) * b[i];` ` ` ` ` `// If both product and a[i] are` ` ` `// negative, we must decrease value` ` ` `// of a[i] to minimize result.` ` ` `else` `if` `(pro < 0 && a[i] < 0)` ` ` `temp = (a[i] - 2 * k) * b[i];` ` ` ` ` `// Similar to above two cases` ` ` `// for positive product.` ` ` `else` `if` `(pro > 0 && a[i] < 0)` ` ` `temp = (a[i] + 2 * k) * b[i];` ` ` `else` `if` `(pro > 0 && a[i] > 0)` ` ` `temp = (a[i] - 2 * k) * b[i];` ` ` ` ` `// Check if current difference` ` ` `// becomes higher than the maximum` ` ` `// difference so far.` ` ` `let d = Math.abs(pro - temp);` ` ` `if` `(d > diff)` ` ` `diff = d; ` ` ` `}` ` ` ` ` `return` `res - diff;` `}` ` ` `// Driver code` ` ` `let a = [ 2, 3, 4, 5, 4 ];` ` ` `let b = [ 3, 4, 2, 3, 2 ];` ` ` `let n = 5, k = 3;` ` ` `document.write(minproduct(a, b, n, k));` ` ` ` ` `// This code is contributed by sanjoy_62.` `</script>` |

## PHP

`<?php` `// PHP program to find minimum sum of product` `// of two arrays with k operations allowed on` `// first array.` `// Function to find the minimum product` `function` `minproduct( ` `$a` `, ` `$b` `, ` `$n` `, ` `$k` `)` `{` ` ` `$diff` `= 0; ` `$res` `= 0;` ` ` `$temp` `;` ` ` `for` `( ` `$i` `= 0; ` `$i` `< ` `$n` `; ` `$i` `++) {` ` ` `// Find product of current` ` ` `// elements and update` ` ` `// result.` ` ` `$pro` `= ` `$a` `[` `$i` `] * ` `$b` `[` `$i` `];` ` ` `$res` `= ` `$res` `+ ` `$pro` `;` ` ` `// If both product and b[i]` ` ` `// are negative, we must` ` ` `// increase value of a[i]` ` ` `// to minimize result.` ` ` `if` `(` `$pro` `< 0 ` `and` `$b` `[` `$i` `] < 0)` ` ` `$temp` `= (` `$a` `[` `$i` `] + 2 * ` `$k` `) *` ` ` `$b` `[` `$i` `];` ` ` `// If both product and` ` ` `// a[i] are negative,` ` ` `// we must decrease value` ` ` `// of a[i] to minimize` ` ` `// result.` ` ` `else` `if` `(` `$pro` `< 0 ` `and` `$a` `[` `$i` `] < 0)` ` ` `$temp` `= (` `$a` `[` `$i` `] - 2 * ` `$k` `) * ` `$b` `[` `$i` `];` ` ` `// Similar to above two` ` ` `// cases for positive` ` ` `// product.` ` ` `else` `if` `(` `$pro` `> 0 ` `and` `$a` `[` `$i` `] < 0)` ` ` `$temp` `= (` `$a` `[` `$i` `] + 2 * ` `$k` `) * ` `$b` `[` `$i` `];` ` ` `else` `if` `(` `$pro` `> 0 ` `and` `$a` `[` `$i` `] > 0)` ` ` `$temp` `= (` `$a` `[` `$i` `] - 2 * ` `$k` `) * ` `$b` `[` `$i` `];` ` ` `// Check if current difference becomes higher` ` ` `// than the maximum difference so far.` ` ` `$d` `= ` `abs` `(` `$pro` `- ` `$temp` `);` ` ` `if` `(` `$d` `> ` `$diff` `)` ` ` `$diff` `= ` `$d` `;` ` ` `}` ` ` `return` `$res` `- ` `$diff` `;` `}` ` ` `// Driver Code` ` ` `$a` `= ` `array` `(2, 3, 4, 5, 4 ,0);` ` ` `$b` `=` `array` `(3, 4, 2, 3, 2);` ` ` `$n` `= 5;` ` ` `$k` `= 3;` ` ` `echo` `minproduct(` `$a` `, ` `$b` `, ` `$n` `, ` `$k` `);` ` ` `// This code is contributed by anuj_67.` `?>` |

**Output :**

```
25
```

** Time Complexity:** O(n)

**O(1)**

**Auxiliary Space:**This article is contributed by ** Abhishek Sharma**. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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