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Number formed by the rightmost set bit in N

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  • Difficulty Level : Easy
  • Last Updated : 04 Jul, 2022

Given an integer N, the task is to find an integer M formed by taking the rightmost set bit in N i.e. the only set bit in M will be the rightmost set bit in N and the rest of the bits will be unset.
Examples: 
 

Input: N = 7 
Output:
7 = 111, the number formed by the last set bit is 001 i.e. 1.
Input: N = 10 
Output:
10 = 1010 -> 0010 = 2
Input: N = 16 
Output: 16 
 

 

Approach: 
 

  • Store x = n & (n – 1) which will unset the first set bit from the right in n.
  • Now, update n = n ^ x to set the changed bit and unset all the others which is the required integer.

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 integer formed
// by taking the rightmost set bit in n
int firstSetBit(int n)
{
 
    // n & (n - 1) unsets the first set
    // bit from the right in n
    int x = n & (n - 1);
 
    // Take xor with the original number
    // The position of the 'changed bit'
    // will be set and rest will be unset
    return (n ^ x);
}
 
// Driver code
int main()
{
    int n = 12;
 
    cout << firstSetBit(n);
 
    return 0;
}

Java




// Java implementation of the approach
class geeks
{
     
    // Function to return the integer formed
    // by taking the rightmost set bit in n
    public static int firstSetBit(int n)
    {
         
        // n & (n - 1) unsets the first set
        // bit from the right in n
        int x = n & (n-1);
         
        // Take xor with the original number
        // The position of the 'changed bit'
        // will be set and rest will be unset
        return (n ^ x);
    }
     
    // Driver Code
    public static void main (String[] args)
    {
        int n = 12;
        System.out.println(firstSetBit(n));
    }
}
 
// This code is contributed by
// sanjeev2552

Python3




# Python3 implementation of the approach
 
# Function to return the integer formed
# by taking the rightmost set bit in n
def firstSetBit(n):
 
    # n & (n - 1) unsets the first set
    # bit from the right in n
    x = n & (n - 1)
 
    # Take xor with the original number
    # The position of the 'changed bit'
    # will be set and rest will be unset
    return (n ^ x)
 
# Driver code
n = 12
 
print(firstSetBit(n))
 
# This code is contributed by mohit kumar 29

C#




// C# implementation of the approach
using System;
 
class geeks
{
     
    // Function to return the integer formed
    // by taking the rightmost set bit in n
    public static int firstSetBit(int n)
    {
         
        // n & (n - 1) unsets the first set
        // bit from the right in n
        int x = n & (n-1);
         
        // Take xor with the original number
        // The position of the 'changed bit'
        // will be set and rest will be unset
        return (n ^ x);
    }
     
    // Driver Code
    public static void Main ()
    {
        int n = 12;
        Console.WriteLine(firstSetBit(n));
    }
}
 
// This code is contributed by
// anuj_67..

Javascript




<script>
// JavaScript implementation of the approach
 
// Function to return the integer formed
// by taking the rightmost set bit in n
function firstSetBit(n)
{
 
    // n & (n - 1) unsets the first set
    // bit from the right in n
    let x = n & (n - 1);
 
    // Take xor with the original number
    // The position of the 'changed bit'
    // will be set and rest will be unset
    return (n ^ x);
}
 
// Driver code
    let n = 12;
    document.write(firstSetBit(n));
 
// This code is contributed by Manoj.
</script>

Output: 

4

 

Time Complexity: O(1)

Auxiliary Space: O(1)


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