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

Difficulty Level : Medium
Last Updated : 07 May, 2021

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.

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.
Toggle all bits of number obtained above using ~ (Bitwise negation)

C++

// 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

// 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;
}

Python3

# 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

Javascript

<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>

Output:

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