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Sum of minimum element of all subarrays of a sorted array
• Difficulty Level : Medium
• Last Updated : 29 Apr, 2021

Given a sorted array A of n integers. The task is to find the sum of the minimum of all possible subarrays of A.

Examples:

Input: A = [ 1, 2, 4, 5]
Output: 23
Subsequences are [1], [2], [4], [5], [1, 2], [2, 4], [4, 5] [1, 2, 4], [2, 4, 5], [1, 2, 4, 5]
Minimums are 1, 2, 4, 5, 1, 2, 4, 1, 2, 1.
Sum is 23
Input: A = [1, 2, 3]
Output: 10

Approach: The Naive approach is to generate all possible subarrays, find their minimum and add them to the result.
Efficient Approach: It is given that the array is sorted, so observe that the minimum element occurs N times, the second minimum occurs N-1 times, and so on… Let’s take an example:

arr[] = {1, 2, 3}
Subarrays are {1}, {2}, {3}, {1, 2}, {2, 3}, {1, 2, 3}
Minimum of each subarray: {1}, {2}, {3}, {1}, {2}, {1}.
where
1 occurs 3 times i.e. n times when n = 3.
2 occurs 2 times i.e. n-1 times when n = 3.
3 occurs 1 times i.e. n-2 times when n = 3.

So, traverse the array and add the current element i.e. (arr[i]* n-i) to the sum.
Below is the implementation of the above approach:

## C++

 `// C++ implementation of the above approach``#include ``using` `namespace` `std;` `// Function to find the sum``// of minimum of all subarrays``int` `findMinSum(``int` `arr[], ``int` `n)``{` `    ``int` `sum = 0;``    ``for` `(``int` `i = 0; i < n; i++)``        ``sum += arr[i] * (n - i);` `    ``return` `sum;``}` `// Driver code``int` `main()``{``    ``int` `arr[] = { 3, 5, 7, 8 };``    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr[0]);` `    ``cout << findMinSum(arr, n);` `    ``return` `0;``}`

## Java

 `// Java implementation of the above approach``class` `GfG``{` `// Function to find the sum``// of minimum of all subarrays``static` `int` `findMinSum(``int` `arr[], ``int` `n)``{` `    ``int` `sum = ``0``;``    ``for` `(``int` `i = ``0``; i < n; i++)``        ``sum += arr[i] * (n - i);` `    ``return` `sum;``}` `// Driver code``public` `static` `void` `main(String[] args)``{``    ``int` `arr[] = { ``3``, ``5``, ``7``, ``8` `};``    ``int` `n = arr.length;` `    ``System.out.println(findMinSum(arr, n));``}``}` `// This code is contributed by Prerna Saini`

## Python3

 `# Python3 implementation of the``# above approach` `# Function to find the sum``# of minimum of all subarrays``def` `findMinSum(arr, n):``    ``sum` `=` `0``    ``for` `i ``in` `range``(``0``, n):``        ``sum` `+``=` `arr[i] ``*` `(n ``-` `i)``    ``return` `sum` `# Driver code``arr ``=` `[``3``, ``5``, ``7``, ``8` `]``n ``=` `len``(arr)` `print``(findMinSum(arr, n))` `# This code has been contributed``# by 29AjayKumar`

## C#

 `// C# implementation of the above approach``using` `System;` `class` `GfG``{` `// Function to find the sum``// of minimum of all subarrays``static` `int` `findMinSum(``int` `[]arr, ``int` `n)``{` `    ``int` `sum = 0;``    ``for` `(``int` `i = 0; i < n; i++)``        ``sum += arr[i] * (n - i);` `    ``return` `sum;``}` `// Driver code``public` `static` `void` `Main(String []args)``{``    ``int` `[]arr = { 3, 5, 7, 8 };``    ``int` `n = arr.Length;` `    ``Console.WriteLine(findMinSum(arr, n));``}``}` `// This code is contributed by Arnab Kundu`

## PHP

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## Javascript

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Output:
`49`

Note: To find the Sum of maximum element of all subarrays in a sorted array, just traverse the array in reverse order and apply the same formula for Sum.

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