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Sum of all mersenne numbers present in an array
  • Difficulty Level : Expert
  • Last Updated : 13 Jun, 2019
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Given an array of integers arr[], the task is to find the sum of all the Mersenne numbers from the array. A number is a Mersenne number if it is greater than 0 and is one less than some power of 2. First few Mersenne numbers are 1, 3, 7, 15, 31, 63, 127, …

Examples:

Input: arr[] = {17, 6, 7, 63, 3}
Output: 73
Only 7, 63 and 3 are Mersenne numbers i.e. 7 + 63 + 3 = 73

Input: arr[] = {1, 3, 11, 45}
Output: 4

Approach: Initialise sum = 0 and start traversing all the elements of the array, if current element is one less than some power of 2 and is greater than 0 then update sum = sum + arr[i]. Print the sum in the end.



Below is the implementation of the above approach:

C++




// C++ implementation of the approach
#include <iostream>
using namespace std;
  
// Function that returns true
// if n is a Mersenne number
int isMersenne(int n)
{
    while (n != 0) 
    {
        int r = n % 2;
        if (r == 0)
            return false;
        n /= 2;
    }
    return true;
}
  
// Function to return the sum of all the
// Mersenne numbers from the given array
int sumOfMersenne(int arr[], int n)
{
  
    // To store the required sum
    int sum = 0;
    for (int i = 0; i < n; i++)
    {
  
        // If current element is a Mersenne number
        if (arr[i] > 0 && isMersenne(arr[i])) 
        {
            sum += arr[i];
        }
    }
    return sum;
}
  
// Driver code
int main()
{
    int arr[] = { 17, 6, 7, 63, 3 };
    int n = sizeof(arr) / sizeof(int);
    cout << (sumOfMersenne(arr, n));
    return 0;
}
  
// This code is contributed by jit_t

Java




// Java implementation of the approach
class GFG {
  
    // Function that returns true
    // if n is a Mersenne number
    static boolean isMersenne(int n)
    {
        while (n != 0) {
            int r = n % 2;
            if (r == 0)
                return false;
            n /= 2;
        }
        return true;
    }
  
    // Function to return the sum of all the
    // Mersenne numbers from the given array
    static int sumOfMersenne(int[] arr, int n)
    {
  
        // To store the required sum
        int sum = 0;
        for (int i = 0; i < n; i++) {
  
            // If current element is a Mersenne number
            if (arr[i] > 0 && isMersenne(arr[i])) {
                sum += arr[i];
            }
        }
        return sum;
    }
  
    // Driver code
    public static void main(String[] args)
    {
        int[] arr = { 17, 6, 7, 63, 3 };
        int n = arr.length;
        System.out.print(sumOfMersenne(arr, n));
    }
}

Python3




# Python3 implementation of the approach 
  
# Function that returns true 
# if n is a Mersenne number 
def isMersenne(n) : 
    while (n != 0) :
        r = n % 2;
        if (r == 0) :
            return False
        n //= 2
          
    return True
  
# Function to return the sum of all the 
# Mersenne numbers from the given array 
def sumOfMersenne(arr, n) : 
    # To store the required sum 
    sum = 0
    for i in range(n) :
  
        # If current element is a Mersenne number 
        if (arr[i] > 0 and isMersenne(arr[i])) :
            sum += arr[i]; 
      
    return sum
  
  
# Driver code 
if __name__ == "__main__"
  
    arr = [17, 6, 7, 63, 3 ];
    n = len(arr); 
    print(sumOfMersenne(arr, n)); 
      
# This code is contributed by AnkitRai01

C#




//C# implementation of the approach
using System;
  
class GFG
{
    // Function that returns true
    // if n is a Mersenne number
    static bool isMersenne(int n)
    {
        while (n != 0) 
        {
            int r = n % 2;
            if (r == 0)
                return false;
            n /= 2;
        }
        return true;
    }
  
    // Function to return the sum of all the
    // Mersenne numbers from the given array
    static int sumOfMersenne(int[] arr, int n)
    {
  
        // To store the required sum
        int sum = 0;
        for (int i = 0; i < n; i++) 
        {
  
            // If current element is a Mersenne number
            if (arr[i] > 0 && isMersenne(arr[i]))
            {
                sum += arr[i];
            }
        }
        return sum;
    }
  
    // Driver code
    static public void Main ()
    {
        int[] arr = { 17, 6, 7, 63, 3 };
        int n = arr.Length;
        Console.WriteLine(sumOfMersenne(arr, n));
    }
}
  
// This code is contributed by jit_t
Output:
73

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