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Product of all Subarrays of an Array | Set 2
• Difficulty Level : Medium
• Last Updated : 05 May, 2021

Given an array arr[] of integers of size N, the task is to find the products of all subarrays of the array.
Examples:

Input: arr[] = {2, 4}
Output: 64
Explanation:
Here, subarrays are {2}, {2, 4}, and {4}.
Products of each subarray are 2, 8, 4.
Product of all Subarrays = 64
Input: arr[] = {1, 2, 3}
Output: 432
Explanation:
Here, subarrays are {1}, {1, 2}, {1, 2, 3}, {2}, {2, 3}, {3}.
Products of each subarray are 1, 2, 6, 2, 6, 3.
Product of all Subarrays = 432

Naive and Iterative approach: Please refer this post for these approaches.
Approach: The idea is to count the number of each element occurs in all the subarrays. To count we have below observations:

• In every subarray beginning with arr[i], there are (N – i) such subsets starting with the element arr[i]
For Example:

For array arr[] = {1, 2, 3}
N = 3 and for element 2 i.e., index = 1
There are (N – index) = 3 – 1 = 2 subsets
{2} and {2, 3}

•
• For any element arr[i], there are (N – i)*i subarrays where arr[i] is not the first element.

For array arr[] = {1, 2, 3}
N = 3 and for element 2 i.e., index = 1
There are (N – index)*index = (3 – 1)*1 = 2 subsets where 2 is not the first element.
{1, 2} and {1, 2, 3}

•

Therefore, from the above observations, the total number of each element arr[i] occurs in all the subarrays at every index i is given by:

```total_elements = (N - i) + (N - i)*i
total_elements = (N - i)*(i + 1) ```

The idea is to multiply each element (N – i)*(i + 1) number of times to get the product of elements in all subarrays.
Below is the implementation of the above approach:

## C++

 `// C++ program for the above approach``#include ``using` `namespace` `std;` `// Function to find the product of``// elements of all subarray``long` `int` `SubArrayProdct(``int` `arr[],``                        ``int` `n)``{``    ``// Initialize the result``    ``long` `int` `result = 1;` `    ``// Computing the product of``    ``// subarray using formula``    ``for` `(``int` `i = 0; i < n; i++)``        ``result *= ``pow``(arr[i],``                      ``(i + 1) * (n - i));` `    ``// Return the product of all``    ``// elements of each subarray``    ``return` `result;``}` `// Driver Code``int` `main()``{``    ``// Given array arr[]``    ``int` `arr[] = { 2, 4 };``    ``int` `N = ``sizeof``(arr) / ``sizeof``(arr);` `    ``// Function Call``    ``cout << SubArrayProdct(arr, N)``         ``<< endl;``    ``return` `0;``}`

## Java

 `// Java program for the above approach``import` `java.util.*;` `class` `GFG{` `// Function to find the product of``// elements of all subarray``static` `int` `SubArrayProdct(``int` `arr[], ``int` `n)``{``    ` `    ``// Initialize the result``    ``int` `result = ``1``;` `    ``// Computing the product of``    ``// subarray using formula``    ``for``(``int` `i = ``0``; i < n; i++)``       ``result *= Math.pow(arr[i], (i + ``1``) *``                                  ``(n - i));` `    ``// Return the product of all``    ``// elements of each subarray``    ``return` `result;``}` `// Driver code``public` `static` `void` `main(String[] args)``{` `    ``// Given array arr[]``    ``int` `arr[] = ``new` `int``[]{``2``, ``4``};` `    ``int` `N = arr.length;` `    ``// Function Call``    ``System.out.println(SubArrayProdct(arr, N));``}``}` `// This code is contributed by Pratima Pandey`

## Python3

 `# Python3 program for the above approach` `# Function to find the product of``# elements of all subarray``def` `SubArrayProdct(arr, n):` `    ``# Initialize the result``    ``result ``=` `1``;` `    ``# Computing the product of``    ``# subarray using formula``    ``for` `i ``in` `range``(``0``, n):``        ``result ``*``=` `pow``(arr[i],``                     ``(i ``+` `1``) ``*` `(n ``-` `i));` `    ``# Return the product of all``    ``# elements of each subarray``    ``return` `result;` `# Driver Code` `# Given array arr[]``arr ``=` `[ ``2``, ``4` `];``N ``=` `len``(arr);` `# Function Call``print``(SubArrayProdct(arr, N))` `# This code is contributed by Code_Mech`

## C#

 `// C# program for the above approach``using` `System;``class` `GFG{` `// Function to find the product of``// elements of all subarray``static` `int` `SubArrayProdct(``int` `[]arr, ``int` `n)``{``    ` `    ``// Initialize the result``    ``int` `result = 1;` `    ``// Computing the product of``    ``// subarray using formula``    ``for``(``int` `i = 0; i < n; i++)``       ``result *= (``int``)(Math.Pow(arr[i], (i + 1) *``                                        ``(n - i)));` `    ``// Return the product of all``    ``// elements of each subarray``    ``return` `result;``}` `// Driver code``public` `static` `void` `Main()``{` `    ``// Given array arr[]``    ``int` `[]arr = ``new` `int``[]{2, 4};` `    ``int` `N = arr.Length;` `    ``// Function Call``    ``Console.Write(SubArrayProdct(arr, N));``}``}` `// This code is contributed by Code_Mech`

## Javascript

 ``
Output:
`64`

Time Complexity: O(N), where N is the number of elements.
Auxiliary Space: O(1)

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