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Toggle the last m bits
  • Difficulty Level : Easy
  • Last Updated : 20 May, 2021

Given a non-negative number n. The problem is to toggle the last m bits in the binary representation of n. A toggle operation flips a bit from 0 to 1 and a bit from 1 to 0.
Constraint: 1 <= m <= n.

Examples: 

Input : n = 21, m = 2
Output : 22
(21)10 = (10101)2
(22)10 = (10110)2
The last two bits in the binary
representation of 21 are toggled.

Input : n = 107, m = 4
Output : 100 

Approach: Following are the steps: 

  1. Calculate num = (1 << m) – 1. This will produce a number num having m bits and all will be set.
  2. Now, perform n = n ^ num. This will toggle the last m bits in n.

C++




// C++ implementation to
// toggle the last m bits
#include <bits/stdc++.h>
using namespace std;
 
// function to toggle
// the last m bits
unsigned int toggleLastMBits
         (unsigned int n, unsigned int m)
{
     
    // calculating a number
    // 'num' having 'm' bits
    // and all are set.
    unsigned int num = (1 << m) - 1;
 
    // toggle the last m bits
    // and return the number
    return (n ^ num);
}
 
// Driver code
int main()
{
    unsigned int n = 107;
    unsigned int m = 4;
    cout << toggleLastMBits(n, m);
    return 0;
}

Java




// Java implementation to
// toggle the last m bits
import java.util.*;
import java.lang.*;
 
public class GfG{
     
    // function to toggle
    // the last m bits
    public static int toggleLastMBits
                      (int n, int m)
    {
         
        // calculating a number
        // 'num' having 'm' bits
        // and all are set
        int num = (1 << m) - 1;
  
        // toggle the last m bits
        // and return the number
        return (n ^ num);
    }
     
    // Driver function
    public static void main(String argc[]){
        int n = 107;
        int m = 4;
        n =  toggleLastMBits(n, m);
        System.out.println(n);
               
    }
}
 
// This code is contributed by Sagar Shukla.

Python3




# Python implementation to
# toggle the last m bits
 
# function to toggle
# the last m bits
def toggleLastMBits(n,m):
 
    # calculating a number
    # 'num' having 'm' bits
    # and all are set.
    num = (1 << m) - 1
  
    # toggle the last m bits
    # and return the number
    return (n ^ num)
 
# Driver code
 
n = 107
m = 4
print(toggleLastMBits(n, m))
 
# This code is contributed
# by Anant Agarwal.

C#




// C# implementation to
// toggle the last m bits
using System;
 
namespace Toggle
{
    public class GFG
    {    
                 
    // Function to toggle the last m bits
    public static int toggleLastMBits(int n, int m)
    {
         
        // Calculating a number 'num' having
        // 'm' bits and all are set
        int num = (1 << m) - 1;
 
        // Toggle the last m bits
        // and return the number
        return (n ^ num);
    }
     
    // Driver Code
    public static void Main() {
         
        int n = 107, m = 4;
        n = toggleLastMBits(n, m);
        Console.Write(n);
                 
    }
    }
}
 
// This code is contributed by Sam007.

PHP




<?php
// PHP implementation to
// toggle the last m bits
 
    // function to toggle
    // the last m bits
    function toggleLastMBits($n, $m)
    {
         
        // calculating a number
        // 'num' having 'm' bits
        // and all are set.
        $num = (1 << $m) - 1;
     
        // toggle the last m bits
        // and return the number
        return ($n ^ $num);
    }
 
// Driver code
{
    $n = 107;
    $m = 4;
    echo toggleLastMBits($n, $m);
    return 0;
}
 
// This code is contributed by nitin mittal.
?>

Javascript




<script>
 
// Javascript implementation to
// toggle the last m bits
 
// function to toggle
// the last m bits
function toggleLastMBits(n, m)
{
     
    // calculating a number
    // 'num' having 'm' bits
    // and all are set.
    var num = (1 << m) - 1;
 
    // toggle the last m bits
    // and return the number
    return (n ^ num);
}
 
// Driver code
var  n = 107;
var  m = 4;
document.write( toggleLastMBits(n, m));
 
</script>

Output: 

100

This article is contributed by Ayush Jauhari. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
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