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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 <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;
}

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




<script>
 
    // Javascript Program to generate
    // Prefix Product Array
     
    // Function to generate
    // prefix product array
    function prefixProduct(a, n)
    {
        // Update the array
        // with the product of
        // prefixes
        for (let i = 1; i < n; i++) {
            a[i] = a[i] * a[i - 1];
        }
 
        // Print the array
        for (let j = 0; j < n; j++) {
            document.write(a[j] + ", ");
        }
 
        return 0;
    }
 
    let arr = [ 2, 4, 6, 5, 10 ];
    let N = arr.length;
    prefixProduct(arr, N);
 
</script>
Output: 
2, 8, 48, 240, 2400

 

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

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