Toggle all the bits of a number except k-th bit.

Given a positive (or unsigned) integer n, write a function to toggle all the bits except k-th bit. Here value of k starts from 0 (zero) and from right. 

Examples:  

Input : n = 4294967295, k = 0
Output : 1
The number 4294967295 in 32 bits has all bits
set.  When we toggle all bits except last bit,
we get 1.

Input  :  n = 1, k = 1
Output : 4294967292
4294967262 has all bits toggled except second
bit from right.

1. Toggle bit at k-th position. We do it by finding a number with only k-th bit set (using 1 << k), then doing bitwise XOR of this number n.
2. Toggle all bits of number obtained above using ~ (Bitwise negation)

// C++ program to toggle all bits except kth bit
#include <iostream>
using namespace std;

// Returns a number with all bit toggled in n
// except k-th bit
unsigned int toggleAllExceptK(unsigned int n,
                              unsigned int k)
{
    
    /* 1) Toggle k-th bit by doing n ^ (1 << k)
       2) Toggle all bits of the modified number */
    return ~(n ^ (1 << k));
}

// Driver code
int main()
{
    unsigned int n = 4294967295;
    unsigned int k = 0;
    
    cout << toggleAllExceptK(n, k);
    
    return 0;
}

// This code is contributed by khushboogoyal499

// C program to toggle all bits except kth bit
#include<stdio.h>

// Returns a number with all bit toggled in n
// except k-th bit
unsigned int toggleAllExceptK(unsigned int n,
                            unsigned int k)
{
   /* 1) Toggle k-th bit by doing n ^ (1 << k)
      2) Toggle all bits of the modified number */
    return ~(n ^ (1 << k));
}

// Driver code
int main()
{
    unsigned int n = 4294967295;
    unsigned int k = 0;
    printf("%u", toggleAllExceptK( n, k));
    return 0;
}

public class Main {
    // Returns a number with all bit toggled in n
    // except k-th bit
    public static long toggleAllExceptK(long n, int k) {
        // 1) Toggle k-th bit by doing n ^ (1 << k)
        // 2) Toggle all bits of the modified number 
        long temp = n ^ (1L << k);
        long mask = (1L << 32) - 1;
        return ~temp & mask;
    }

    // Driver code
    public static void main(String[] args) {
        long n = 4294967295L;
        int k = 0;
        System.out.println(toggleAllExceptK(n, k));
    }
}

# Python3 program to toggle all bits
# except kth bit

# Returns a number with all bit toggled
# in n except k-th bit
def toggleAllExceptK(n, k):
    
    # 1) Toggle k-th bit by doing n ^ (1 << k)
    # 2) Toggle all bits of the modified number 
    temp = bin(n ^ (1 << k))[2:]

    ans = ""

    for i in temp:
        if i == '1':
            ans += '0'
        else:
            ans += '1'

    return int(ans, 2)

# Driver code
if __name__ == '__main__':
    
    n = 4294967295
    k = 0
    
    print(toggleAllExceptK(n, k))

# This code is contributed by mohit kumar 29

<script>
// javascript program to toggle all bits except kth bit
    
    // Returns a number with all bit toggled in n
    // except k-th bit
    function toggleAllExceptK(n,k)
    {
        /* 1) Toggle k-th bit by doing n ^ (1 << k)
           2) Toggle all bits of the modified number */
        return ~(n ^ (1 << k));
    }
    
    // Driver code
    let n = 4294967295;
    let k = 0;
    document.write(toggleAllExceptK(n, k));
    
    
    //This code is contributed by unknown2108
    
</script>

// C# equivalent code
using System;

public class Program
{
    // Returns a number with all bit toggled in n
    // except k-th bit
    public static long toggleAllExceptK(long n, int k)
    {
        // 1) Toggle k-th bit by doing n ^ (1 << k)
        long temp = n ^ (1L << k);
        // 2) Toggle all bits of the modified number 
        long mask = (1L << 32) - 1;
        return ~temp & mask;
    }

    // Driver code
    public static void Main(string[] args)
    {
        long n = 4294967295L;
        int k = 0;
        Console.WriteLine(toggleAllExceptK(n, k));
    }
}

Output: 

1

Time Complexity : O(1)

Space Complexity : O(1)