Number of pairs with Bitwise OR as Odd number

Given an array A[] of size N. The task is to find how many pair(i, j) exists such that A[i] OR A[j] is odd.
Examples: 

Input : N = 4
            A[] = { 5, 6, 2, 8 }
Output : 3
Explanation :
Since pair of A[] = ( 5, 6 ), ( 5, 2 ), ( 5, 8 ),
( 6, 2 ), ( 6, 8 ), ( 2, 8 )
5 OR 6 = 7, 5 OR 2 = 7, 5 OR 8 = 13
6 OR 2 = 6, 6 OR 8 = 14, 2 OR 8 = 10
Total pair A( i, j ) = 6 and Odd = 3

Input : N = 7
            A[] = {8, 6, 2, 7, 3, 4, 9}
Output :15

A Simple Solution is to check every pair and find the Bitwise-OR and count all such pairs with Bitwise OR as odd.
Below is the implementation of the above approach: 

C++

// C++ program to count pairs with odd OR

#include <iostream>
using namespace std;

// Function to count pairs with odd OR
int findOddPair(int A[], int N)
{
    int oddPair = 0;
    for (int i = 0; i < N; i++) {
        for (int j = i + 1; j < N; j++) {

            // find OR operation
            // check odd or odd
            if ((A[i] | A[j]) % 2 != 0)
                oddPair++;
        }
    }

    // return count of odd pair
    return oddPair;
}

// Driver Code
int main()
{
    int A[] = { 5, 6, 2, 8 };

    int N = sizeof(A) / sizeof(A[0]);

    cout << findOddPair(A, N) << endl;

    return 0;
}

C

// C program to count pairs with odd OR
#include <stdio.h>

// Function to count pairs with odd OR
int findOddPair(int A[], int N)
{
    int oddPair = 0;
    for (int i = 0; i < N; i++) {
        for (int j = i + 1; j < N; j++) {

            // find OR operation
            // check odd or odd
            if ((A[i] | A[j]) % 2 != 0)
                oddPair++;
        }
    }

    // return count of odd pair
    return oddPair;
}

// Driver Code
int main()
{
    int A[] = { 5, 6, 2, 8 };

    int N = sizeof(A) / sizeof(A[0]);

    printf("%d\n",findOddPair(A, N));
    return 0;
}

// This code is contributed by kothavvsaakash.

Java

// Java program to count pairs
// with odd OR
class GFG
{
// Function to count pairs with odd OR
static int findOddPair(int A[], int N)
{
    int oddPair = 0;
    for (int i = 0; i < N; i++)
    {
        for (int j = i + 1; j < N; j++)
        {

            // find OR operation
            // check odd or odd
            if ((A[i] | A[j]) % 2 != 0)
                oddPair++;
        }
    }

    // return count of odd pair
    return oddPair;
}

// Driver Code
public static void main(String []args)
{
    int A[] = { 5, 6, 2, 8 };

    int N = A.length;

    System.out.println(findOddPair(A, N));
}
}

// This code is contributed by ANKITRAI1

Python3

# Python3 program to count pairs with odd OR


# Function to count pairs with odd OR
def findOddPair(A, N):

    oddPair = 0
    for i in range(0, N):
        for j in range(i+1, N):

            # find OR operation
            # check odd or odd
            if ((A[i] | A[j]) % 2 != 0):
                oddPair+=1

    # return count of odd pair
    return oddPair


# Driver Code
def main():

    A = [ 5, 6, 2, 8 ]

    N = len(A)

    print(findOddPair(A, N))

if __name__ == '__main__':
    main()
# This code is contributed by PrinciRaj1992

C#

// C#  program to count pairs
// with odd OR

using System;

public class GFG{

    // Function to count pairs with odd OR
static int findOddPair(int[] A, int N)
{
    int oddPair = 0;
    for (int i = 0; i < N; i++)
    {
        for (int j = i + 1; j < N; j++)
        {

            // find OR operation
            // check odd or odd
            if ((A[i] | A[j]) % 2 != 0)
                oddPair++;
        }
    }

    // return count of odd pair
    return oddPair;
}

// Driver Code
    static public void Main (){
    int []A = { 5, 6, 2, 8 };
    int N = A.Length;

    Console.WriteLine(findOddPair(A, N));
    }
}

//This code is contributed by ajit

PHP

<?php
//PHP program to count pairs with odd OR

// Function to count pairs with odd OR
function  findOddPair($A, $N)
{
    $oddPair = 0;
    for ($i = 0; $i < $N; $i++) {
        for ($j = $i + 1; $j < $N; $j++) {

            // find OR operation
            // check odd or odd
            if (($A[$i] | $A[$j]) % 2 != 0)
                $oddPair++;
        }
    }

    // return count of odd pair
    return $oddPair;
}

// Driver Code
    $A = array (5, 6, 2, 8 );
    $N = sizeof($A) / sizeof($A[0]);

    echo findOddPair($A, $N),"\n";



#This code is contributed by ajit
?>

Javascript

<script>
// Javascript program to count pairs with odd OR

// Function to count pairs with odd OR
function findOddPair(A, N)
{
    let oddPair = 0;
    for (let i = 0; i < N; i++)
    {
        for (let j = i + 1; j < N; j++)
        {

            // find OR operation
            // check odd or odd
            if ((A[i] | A[j]) % 2 != 0)
                oddPair++;
        }
    }

    // return count of odd pair
    return oddPair;
}

// Driver Code
let A = [ 5, 6, 2, 8 ];
let N = A.length;
document.write(findOddPair(A, N));

// This code is contributed by souravmahato348.
</script>

Output:

3

Time Complexity: O(N²)

Auxiliary Space: O(1)

An Efficient Solution is to count pairs with even OR and subtract them with a total number of pairs to get pairs with odd Bitwise-OR. To do this, count numbers with last bit as 0. Then a number of pairs with even Bitwise-OR = count * (count – 1)/2 and total number of pairs will be N*(N-1)/2. 
Therefore, pairs with ODD Bitwise-OR will be: 

Total Pairs - Pairs with EVEN Bitwise-OR

Below is the implementation of the above approach:

C++

// C++ program to count pairs with odd OR
#include <iostream>
using namespace std;

// Function to count pairs with odd OR
int countOddPair(int A[], int N)
{
    // Count total even numbers in
    // array

    int count = 0;
    for (int i = 0; i < N; i++)
        if (!(A[i] & 1))
            count++;

    // Even pair count
    int evenPairCount = count * (count - 1) / 2;

    // Total pairs
    int totPairs = N * (N - 1) / 2;

    // Return Odd pair count
    return totPairs - evenPairCount;
}

// Driver main
int main()
{
    int A[] = { 5, 6, 2, 8 };
    int N = sizeof(A) / sizeof(A[0]);

    cout << countOddPair(A, N) << endl;

    return 0;
}

Java

// Java program to count pairs with odd OR

public class GFG {

// Function to count pairs with odd OR
    static int countOddPair(int A[], int N) {
        // Count total even numbers in
        // array

        int count = 0;
        for (int i = 0; i < N; i++) {
            if ((A[i] % 2 != 1)) {
                count++;
            }
        }

        // Even pair count
        int evenPairCount = count * (count - 1) / 2;

        // Total pairs
        int totPairs = N * (N - 1) / 2;

        // Return Odd pair count
        return totPairs - evenPairCount;
    }

// Driver main
    public static void main(String[] args) {
        int A[] = {5, 6, 2, 8};
        int N = A.length;

        System.out.println(countOddPair(A, N));

    }
}

Python3

# Python 3program to count pairs with odd OR

# Function to count pairs with odd OR
def countOddPair(A, N):

    # Count total even numbers in
    # array
    count = 0
    for i in range(0, N):
        if (A[i] % 2 != 1):
            count+=1

    # Even pair count
    evenPairCount = count * (count - 1) / 2

    # Total pairs
    totPairs = N * (N - 1) / 2

    # Return Odd pair count
    return (int)(totPairs - evenPairCount)

# Driver Code
A = [ 5, 6, 2, 8 ]

N = len(A)

print(countOddPair(A, N))

# This code is contributed by PrinciRaj1992

C#

// C# program to count pairs with odd OR
using System;

public class GFG {

// Function to count pairs with odd OR
    static int countOddPair(int []A, int N) {
        // Count total even numbers in
        // array

        int count = 0;
        for (int i = 0; i < N; i++) {
            if ((A[i] % 2 != 1)) {
                count++;
            }
        }

        // Even pair count
        int evenPairCount = count * (count - 1) / 2;

        // Total pairs
        int totPairs = N * (N - 1) / 2;

        // Return Odd pair count
        return totPairs - evenPairCount;
    }

// Driver main
    public static void Main() {
        int []A = {5, 6, 2, 8};
        int N = A.Length;

        Console.WriteLine(countOddPair(A, N));

    }
}
/*This code is contributed by PrinciRaj1992*/

PHP

<?php
// PHP program to count pairs with odd OR
// Function to count pairs with odd OR
function countOddPair( $A, $N)
{
    // Count total even numbers
    // in array
    $count = 0;
    for ($i = 0; $i < $N; $i++)
        if (!($A[$i] & 1))
            $count++;

    // Even pair count
    $evenPairCount = $count *
                    ($count - 1) / 2;

    // Total pairs
    $totPairs = $N * ($N - 1) / 2;

    // Return Odd pair count
    return ($totPairs - $evenPairCount);
}

// Driver main
$A = array( 5, 6, 2, 8 );
$N = sizeof($A);

echo countOddPair($A, $N),"\n";

// This code is contributed by Sach_Code
?>

Javascript

<script>

// Javascript program to count
// pairs with odd OR

// Function to count pairs with odd OR
function countOddPair(A, N)
{
    // Count total even numbers in
    // array

    let count = 0;
    for (let i = 0; i < N; i++)
        if (!(A[i] & 1))
            count++;

    // Even pair count
    let evenPairCount =
    parseInt(count * (count - 1) / 2);

    // Total pairs
    let totPairs = parseInt(N * (N - 1) / 2);

    // Return Odd pair count
    return totPairs - evenPairCount;
}

// Driver main
    let A = [ 5, 6, 2, 8 ];
    let N = A.length;

    document.write(countOddPair(A, N));


</script>

Output:

3

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