Count of values of x <= n for which (n XOR x) = (n – x)

Given an integer n, the task is to find the number of possible values of 0 ? x ? n which satisfy n XOR x = n – x.

Examples:

Input: n = 5 
Output: 4 
Following values of x satisfy the equation 
5 XOR 0 = 5 – 0 = 5 
5 XOR 1 = 5 – 1 = 4 
5 XOR 4 = 5 – 4 = 1 
5 XOR 5 = 5 – 5 = 0

Input: n = 2 
Output: 2 

Naive approach: The easy approach is to check for all values from 0 to n (both inclusive) and finding whether they satisfy the equation. The below code implements this approach:

Below is the implementation of the above approach:  

C++

// C++ implementation of the approach
#include<bits/stdc++.h>
using namespace std;

// Function to return the count of
// valid values of x
static int countX(int n)
{
    int count = 0;

    for (int i = 0; i <= n; i++)
    {

        // If n - x = n XOR x
        if (n - i == (n ^ i))
                count++;
    }

        // Return the required count;
        return count;
}

// Driver code
int main()
{
    int n = 5;
    int answer = countX(n);
    cout << answer;
}

// This code is contributed by
// Shivi_Aggarwal

Java

// Java implementation of the approach
public class GFG {

    // Function to return the count of
    // valid values of x
    static int countX(int n)
    {
        int count = 0;

        for (int i = 0; i <= n; i++) {

            // If n - x = n XOR x
            if (n - i == (n ^ i))
                count++;
        }

        // Return the required count;
        return count;
    }

    // Driver code
    public static void main(String args[])
    {
        int n = 5;
        int answer = countX(n);
        System.out.println(answer);
    }
}

Python3

# Python3 implementation of the approach
import math as mt

# Function to return the count of
# valid values of x
def countX(n):
    count = 0

    for i in range(n + 1):

        if n - i == (n ^ i):
            count += 1

    return count

# Driver Code
if __name__ == '__main__':
    n = 5
    answer = countX(n)
    print(answer)

# This code is contributed by
# Mohit kumar 29

C#

// C# implementation of the above approach
using System;

class GFG
{

    // Function to return the count of
    // valid values of x
    static int countX(int n)
    {
        int count = 0;

        for (int i = 0; i <= n; i++)
        {

            // If n - x = n XOR x
            if (n - i == (n ^ i))
                count++;
        }

        // Return the required count;
        return count;
    }

    // Driver code
    public static void Main()
    {
        int n = 5;
        int answer = countX(n);
        Console.WriteLine(answer);
    }
}

// This code is contributed by Ryuga

PHP

<?php
// PHP implementation of the approach

// Function to return the count of
// valid values of x
function countX($n)
{
    $count = 0;

    for ($i = 0; $i <= $n; $i++)
    {

        // If n - x = n XOR x
        if ($n - $i == ($n ^ $i))
            $count++;
    }

    // Return the required count;
    return $count;
}

// Driver code
$n = 5;
$answer = countX($n);
echo($answer);

// This code is Contributed
// by Mukul Singh.
?>

Javascript

<script>

// Javascript implementation of the approach

// Function to return the count of
// valid values of x
function countX(n)
{
    let count = 0;

    for (let i = 0; i <= n; i++)
    {

        // If n - x = n XOR x
        if (n - i == (n ^ i))
                count++;
    }

        // Return the required count;
        return count;
}

// Driver code
    let n = 5;
    let answer = countX(n);
    document.write(answer);

</script>

Output:

4

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

Efficient Approach: Convert n to its binary representation. Now, for every 1 in the binary string whether we subtract 1 or 0 from it, it will be equivalent to XOR of 1 with 0 or 1 i.e. 
(1 – 1) = (1 XOR 1) = 0
(1 – 0) = (1 XOR 0) = 1
But 0 doesn’t satisfy this condition. So, we only need to consider all the ones in the binary representation of n. Now, for every 1 there are two possibilities, either 0 or 1. Thus if we have m number of 1’s in n then our solution would be 2^m.

Below is the implementation of the above approach:  

C++

// C++ implementation of the approach
#include<bits/stdc++.h>
using namespace std;

// Function to return the count of
// valid values of x
int countX(int n)
{
    // Convert n into binary String
    string binary = bitset<8>(n).to_string();

    // To store the count of 1s
    int count = 0;
    for (int i = 0; i < binary.length(); i++)
    {
        // If current bit is 1
        if (binary.at(i) == '1')
            count++;
    }

    // Calculating answer
    int answer = (int)pow(2, count);
    return answer;
}

// Driver code
int main()
{
    int n = 5;
    int answer = countX(n);
    cout << (answer);
}

// This code is contributed by Rajput-Ji

Java

// Java implementation of the approach
public class GFG {

    // Function to return the count of
    // valid values of x
    static int countX(int n)
    {
        // Convert n into binary String
        String binary = Integer.toBinaryString(n);

        // To store the count of 1s
        int count = 0;

        for (int i = 0; i < binary.length(); i++) {

            // If current bit is 1
            if (binary.charAt(i) == '1')
                count++;
        }

        // Calculating answer
        int answer = (int)Math.pow(2, count);
        return answer;
    }

    // Driver code
    public static void main(String args[])
    {
        int n = 5;
        int answer = countX(n);
        System.out.println(answer);
    }
}

Python3

# Python3 implementation of the approach

# Function to return the count of
# valid values of x
def countX(n):

    # Convert n into binary String
    binary = "{0:b}".format(n)

    # To store the count of 1s
    count = 0

    for i in range(len(binary)):

        # If current bit is 1
        if (binary[i] == '1'):
            count += 1

    # Calculating answer
    answer = int(pow(2, count))
    return answer

# Driver code
if __name__ == "__main__":

    n = 5
    answer = countX(n)
    print(answer)

# This code is contributed by ita_c

C#

// C# implementation of the approach
using System;

class GFG
{

// Function to return the count of
// valid values of x
static int countX(int n)
{
    // Convert n into binary String
    string binary = Convert.ToString(n, 2);

    // To store the count of 1s
    int count = 0;

    for (int i = 0; i < binary.Length; i++)
    {

        // If current bit is 1
        if (binary[i] == '1')
            count++;
    }

    // Calculating answer
    int answer = (int)Math.Pow(2, count);
    return answer;
}

// Driver code
public static void Main()
{
    int n = 5;
    int answer = countX(n);
    Console.WriteLine(answer);
}
}

// This code is contributed
// by Akanksha Rai

Javascript

<script>

// Javascript implementation of the approach

// Function to return the count of
// valid values of x
function countX(n)
{

    // Convert n into binary String
    let binary = (n >>> 0).toString(2);

    // To store the count of 1s
    let count = 0;

    for(let i = 0; i < binary.length; i++)
    {

        // If current bit is 1
        if (binary[i] == '1')
            count++;
    }

    // Calculating answer
    let answer = Math.floor(Math.pow(2, count));
    return answer;
}

// Driver code
let n = 5;
let answer = countX(n);

document.write(answer);

// This code is contributed by avanitrachhadiya2155

</script>

Output:

4

Time complexity:
 Auxiliary Space: O(1)