Prefix Product Array

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++

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// C++ Program to generate
// Prefix Product Array
#include <bits/stdc++.h>
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;
}

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Java

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// 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

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Python3

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# 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

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C#

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// 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

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Output:

2, 8, 48, 240, 2400


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

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