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Product of all the Composite Numbers in an array in C++
Given an array arr[n] of n number of integers, the task is to find the product of all composite numbers in an array.
Composite numbers are the whole numbers which are made by multiplying 2 other whole numbers. For example 6 is a composite number which can be made by multiplying 2 and 3 which are whole numbers. Also we can say they are not prime.
Input
arr[] = {1, 2, 4, 5, 6, 7}Output
24
Explanation − the composite numbers in the array are 4 and 6 and their product is 24.
Input
arr[] = {10, 2, 4, 5, 6, 11}Output
240
Explanation − the composite numbers in the array are 10, 4, 6 and their Product is 240.
Approach used below is as follows to solve the problem
Iterate every element of an array.
Find for the non-prime or composite numbers, i.e. divisible by some other number except 1.
Multiply all the composite numbers.
Return the result.
Algorithm
Start Step 1→ Declare function to find the product of consecutive numbers in array int product_arr(int arr[], int size) declare int max = *max_element(arr, arr + size) set vector<bool> prime(max + 1, true) set prime[0] = true set prime[1] = true Loop For int i = 2 and i * i <= max and i++ IF (prime[i] == true) Loop For int j = i * 2 and j <= max and j += i Set prime[j] = false End End End Set int product = 1 Loop For int i = 0 and i < size and i++ IF (!prime[arr[i]]) Set product *= arr[i] End End return product Stop
Example
#include <bits/stdc++.h>
using namespace std;
//function to find product of consecutive numbers in an array
int product_arr(int arr[], int size){
int max = *max_element(arr, arr + size);
vector<bool> prime(max + 1, true);
prime[0] = true;
prime[1] = true;
for (int i = 2; i * i <= max; i++){
if (prime[i] == true){
for (int j = i * 2; j <= max; j += i)
prime[j] = false;
}
}
int product = 1;
for (int i = 0; i < size; i++)
if (!prime[arr[i]]){
product *= arr[i];
}
return product;
}
int main(){
int arr[] = { 2, 4, 6, 8, 10};
int size = sizeof(arr) / sizeof(arr[0]);
cout<<"product of consecutive numbers in an array: "<<product_arr(arr, size);
return 0;
}Output
If run the above code it will generate the following output −
product of consecutive numbers in an array: 1920
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