Maximum sum of a subsequence whose Bitwise AND is non-zero

Given an array arr[] consisting of N integers, the task is to find the maximum sum of any subsequence from the array having Bitwise AND of its elements not equal to zero.

Examples:

Input: arr[] = {5, 4, 1, 7, 11}
Output: 24
Explanation:
Subsequence with maximum sum is the entire array. Bitwise AND of the array is 0. Hence, the subsequence cannot be considered. 
Subsequence with next greater sum is {5, 1, 7, 11}. Since the Bitwise AND of this subsequence is non-zero, the sum of this subsequence (= 24) is the required answer. 

Input: arr[] = {5, 6, 2}
Output: 11

Naive Approach: The simplest approach to solve the given problem is to generate all possible subsequences of the given array and print the maximum sum of that subsequence having Bitwise AND of all the elements of the subsequence non-zero.

Time Complexity: O(2^N)
Auxiliary Space: O(1)

Efficient Approach: The above approach can also be optimized by observing the fact that the sum of only those elements whose bits are set in all the chosen array elements gives the subsequence whose Bitwise AND is non-zero. Therefore, the idea is to maximize the sum of all those elements. Follow the following steps below to solve the problem:

• Initialize a variable, say ans that stores the maximum sum of subsequences having the value of Bitwise AND as positive.
• Iterate over the range [0, 32] using the variable i and perform the following steps:
  • Initialize a variable, say sum that stores the sum of all the elements whose i^th bit is set.
  • Traverse the given array and if the i^th bit is set of the array element arr[i], then add this value to the variable sum.
  • Update the value of ans to the maximum of ans and sum.
• After completing the above steps, print the value of the sum as the resultant maximum sum of subsequence.

Below is the implementation of our approach:

C++

// C++ program for the above approach

#include <bits/stdc++.h>
using namespace std;

// Function to find the maximum sum of
// a subsequence whose Bitwise AND is non-zero
int maximumSum(int arr[], int N)
{
    // Stores the resultant maximum
    // sum of the subsequence
    int ans = 0;

    // Iterate over all the bits
    for (int bit = 0; bit < 32; bit++) {

        // Stores the sum of array
        // elements whose i-th bit is set
        int sum = 0;

        // Traverse the array elements
        for (int i = 0; i < N; i++) {

            // If the bit is set, then
            // add its value to the sum
            if (arr[i] & (1 << bit)) {
                sum += arr[i];
            }
        }

        // Update the resultant
        // maximum sum
        ans = max(ans, sum);
    }

    // Return the maximum sum
    return ans;
}

// Driver Code
int main()
{
    int arr[] = { 5, 4, 1, 7, 11 };
    int N = sizeof(arr) / sizeof(arr[0]);
    cout << maximumSum(arr, N);

    return 0;
}

Java

// Java program for the above approach
public class GFG
{

 // Function to find the maximum sum of
 // a subsequence whose Bitwise AND is non-zero
 static int maximumSum(int arr[], int N)
 {

     // Stores the resultant maximum
     // sum of the subsequence
     int ans = 0;

     // Iterate over all the bits
     for (int bit = 0; bit < 32; bit++) {

         // Stores the sum of array
         // elements whose i-th bit is set
         int sum = 0;

         // Traverse the array elements
         for (int i = 0; i < N; i++) {

             // If the bit is set, then
             // add its value to the sum
             if ((arr[i] & (1 << bit)) == 1) {
                 sum += arr[i];
             }
         }

         // Update the resultant
         // maximum sum
         ans = Math.max(ans, sum);
     }

     // Return the maximum sum
     return ans;
 }

    // Driver code
    public static void main(String[] args)
    {
        int arr[] = { 5, 4, 1, 7, 11 };
        int N = arr.length;
       System.out.println(maximumSum(arr, N));
    }
}

// This code is contributed by abhinavjain194

Python3

# python3 program for the above approach

# Function to find the maximum sum of
# a subsequence whose Bitwise AND is non-zero
def maximumSum(arr, N):

    # Stores the resultant maximum
    # sum of the subsequence
    ans = 0

    # Iterate over all the bits
    for bit in range(32):

        # Stores the sum of array
        # elements whose i-th bit is set
        sum = 0

        # Traverse the array elements
        for i in range(N):

            # If the bit is set, then
            # add its value to the sum
            if (arr[i] & (1 << bit)):
                sum += arr[i]

        # Update the resultant
        # maximum sum
        ans = max(ans, sum)

    # Return the maximum sum
    return ans

# Driver Code
if __name__ == '__main__':
    arr = [5, 4, 1, 7, 11]
    N = len(arr)
    print(maximumSum(arr, N))

    # This code is contributed by bgangwar59.

C#

// C# program for the above approach
using System;

class GFG{

// Function to find the maximum sum of
// a subsequence whose Bitwise AND is non-zero
static int maximumSum(int[] arr, int N)
{

    // Stores the resultant maximum
    // sum of the subsequence
    int ans = 0;

    // Iterate over all the bits
    for(int bit = 0; bit < 32; bit++)
    {

        // Stores the sum of array
        // elements whose i-th bit is set
        int sum = 0;

        // Traverse the array elements
        for(int i = 0; i < N; i++)
        {

            // If the bit is set, then
            // add its value to the sum
            if ((arr[i] & (1 << bit)) != 0)
            {
                sum += arr[i];
            }
        }

        // Update the resultant
        // maximum sum
        ans = Math.Max(ans, sum);
    }

    // Return the maximum sum
    return ans;
}

// Driver code
static public void Main()
{
    int[] arr = { 5, 4, 1, 7, 11 };
    int N = arr.Length;

    Console.Write(maximumSum(arr, N));
}
}

// This code is contributed by offbeat

Javascript

<script>

// JavaScript program for the above approach

// Function to find the maximum sum of
// a subsequence whose Bitwise AND is non-zero
function maximumSum(arr, N)
{
    // Stores the resultant maximum
    // sum of the subsequence
    let ans = 0;

    // Iterate over all the bits
    for (let bit = 0; bit < 32; bit++) {

        // Stores the sum of array
        // elements whose i-th bit is set
        let sum = 0;

        // Traverse the array elements
        for (let i = 0; i < N; i++) {

            // If the bit is set, then
            // add its value to the sum
            if (arr[i] & (1 << bit)) {
                sum += arr[i];
            }
        }

        // Update the resultant
        // maximum sum
        ans = Math.max(ans, sum);
    }

    // Return the maximum sum
    return ans;
}

// Driver Code
    let arr = [ 5, 4, 1, 7, 11 ];
    let N = arr.length;
    document.write(maximumSum(arr, N));

</script>

Output:

24

Time Complexity: O(N*32)
Auxiliary Space: O(1)