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# Prefix Product Array

• Difficulty Level : Hard
• Last Updated : 26 Mar, 2021

Given an array arr[] of N integers the task is to generate a prefix product array from the given array.

In a prefix product array, ith term pref[i] = arr[i] * arr[i – 1] * …… * arr[0]

Examples:

Input: {1, 2, 3, 4, 5}
Output: {1, 2, 6, 24, 120}
Explanation:
The Prefix Product Array will be {1, 2*1, 3*2*1, 4*3*2*1, 5*4*3*2*1} = {1, 2, 6, 24, 120}
Input: {2, 4, 6, 5, 10}
Output: {2, 8, 48, 240, 2400}

Approach:
Follow the steps below to solve the problem:

• Iterate over the given array from indices 1 to N – 1

• Calculate arr[i] = arr[i] * arr[i-1] for every ith index.

• Finally, print the prefix product array.

Below is the implementation of the above approach.

## C++

 `// C++ Program to generate``// Prefix Product Array``#include ``using` `namespace` `std;` `// Function to generate``// prefix product array``int` `prefixProduct(``int` `a[],``                  ``int` `n)``{``    ``// Update the array``    ``// with the product of``    ``// prefixes``    ``for` `(``int` `i = 1; i < n; i++) {``        ``a[i] = a[i] * a[i - 1];``    ``}` `    ``// Print the array``    ``for` `(``int` `j = 0; j < n; j++) {``        ``cout << a[j] << ``", "``;``    ``}` `    ``return` `0;``}` `// Driver Code``int` `main()``{``    ``int` `arr[] = { 2, 4, 6, 5, 10 };``    ``int` `N = ``sizeof``(arr) / ``sizeof``(arr[0]);``    ``prefixProduct(arr, N);` `    ``return` `0;``}`

## Java

 `// Java program to generate``// Prefix Product Array``class` `GFG{` `// Function to generate``// prefix product array``static` `int` `prefixProduct(``int` `[]a, ``int` `n)``{``    ` `    ``// Update the array``    ``// with the product of``    ``// prefixes``    ``for``(``int` `i = ``1``; i < n; i++)``    ``{``       ``a[i] = a[i] * a[i - ``1``];``    ``}` `    ``// Print the array``    ``for``(``int` `j = ``0``; j < n; j++)``    ``{``       ``System.out.print(a[j] + ``", "``);``    ``}``    ` `    ``return` `0``;``}` `// Driver Code``public` `static` `void` `main (String[] args)``{``    ``int` `arr[] = ``new` `int``[]{ ``2``, ``4``, ``6``, ``5``, ``10` `};``    ``int` `N = ``5``;``    ` `    ``prefixProduct(arr, N);``}``}` `// This code is contributed by Ritik Bansal`

## Python3

 `# Python3 Program to generate``# Prefix Product Array` `# Function to generate``# prefix product array``def` `prefixProduct(a, n):` `    ``# Update the array``    ``# with the product of``    ``# prefixes``    ``for` `i ``in` `range``(``1``, n):``        ``a[i] ``=` `a[i] ``*` `a[i ``-` `1``];``    ` `    ``# Print the array``    ``for` `j ``in` `range``(``0``, n):``        ``print``(a[j], end ``=` `", "``);``    ` `    ``return` `0``;` `# Driver Code``arr ``=` `[ ``2``, ``4``, ``6``, ``5``, ``10` `];``N ``=` `len``(arr);``prefixProduct(arr, N);` `# This code is contributed by Code_Mech`

## C#

 `// C# program to generate``// Prefix Product Array``using` `System;``class` `GFG{` `// Function to generate``// prefix product array``static` `int` `prefixProduct(``int` `[]a, ``int` `n)``{``    ` `    ``// Update the array``    ``// with the product of``    ``// prefixes``    ``for``(``int` `i = 1; i < n; i++)``    ``{``        ``a[i] = a[i] * a[i - 1];``    ``}` `    ``// Print the array``    ``for``(``int` `j = 0; j < n; j++)``    ``{``        ``Console.Write(a[j] + ``", "``);``    ``}``    ``return` `0;``}` `// Driver Code``public` `static` `void` `Main (``string``[] args)``{``    ``int` `[]arr = ``new` `int``[]{ 2, 4, 6, 5, 10 };``    ``int` `N = 5;``    ` `    ``prefixProduct(arr, N);``}``}` `// This code is contributed by rock_cool`

## Javascript

 ``
Output:
`2, 8, 48, 240, 2400`

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

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