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Change all even bits in a number to 0

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  • Difficulty Level : Medium
  • Last Updated : 22 Jun, 2022
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Given a number, change all bits at even positions to 0.

Examples: 

Input : 30
Output : 10
Binary representation of 11110. 
Bits at Even positions are highlighted. 
After making all of them 0, we get 01010

Input :  10
Output :  10

Method 1 (Bit Traversal)

The idea is to traverse through all even bits. We accumulate all powers of 2 in a number to subtract. Finally we subtract the accumulated value from n to obtain the result. 

C++




// C++ program to change even
// bits to 0.
#include <bits/stdc++.h>
using namespace std;
 
// Returns modified number with
// all even bits 0.
int changeEvenBits(int n)
{
    // To store sum of bits
    // at even positions.
    int to_subtract = 0;
 
    // To store bits to shift
    int m = 0;
 
    // One by one put all even
    // bits to end
    for (int x = n; x; x >>= 2) {
        // If current last bit
        // is set, add it to ans
        if (x & 1)
            to_subtract += (1 << m);
 
        // Next shift position
        m += 2;
    }
 
    return n - to_subtract;
}
 
// Driver code
int main()
{
    int n = 30;
    cout << changeEvenBits(n) << endl;
 
    return 0;
}

Java




// Java program to change even
// bits to 0.
import java.util.*;
class GFG {
    // Returns modified number with
    // all even bits 0.
    static int changeEvenBits(int n)
    {
        // To store sum of bits
        // at even positions.
        int to_subtract = 0;
 
        // To store bits to shift
        int m = 0;
 
        // One by one put all even
        // bits to end
        for (int x = n; x > 0; x >>= 2) {
            // If current last bit
            // is set, add it to ans
            if ((x & 1) > 0)
                to_subtract += (1 << m);
 
            // Next shift position
            m += 2;
        }
 
        return n - to_subtract;
    }
 
    // Driver code
    public static void main(String[] args)
    {
        int n = 30;
        System.out.println(changeEvenBits(n));
    }
}
/* This code is contributed by Mr. Somesh Awasthi */

Python3




# Python program to change even
# bits to 0.
 
# Returns modified number with
# all even bits 0.
 
 
def changeEvenBits(n):
 
    # To store sum of bits
    # at even positions.
    to_subtract = 0
 
    # To store bits to shift
    m = 0
 
    # One by one put all even
    # bits to end
    x = n
    while(x):
 
        # If current last bit
        # is set, add it to ans
        if (x & 1):
            to_subtract += (1 << m)
 
        # Next shift position
        m += 2
        x >>= 2
 
    return n - to_subtract
 
 
# Driver code
n = 30
print(changeEvenBits(n))
 
# This code is contributed by Sachin Bisht

C#




// C# program to change even
// bits to 0.
using System;
 
class GFG {
     
    // Returns modified number with
    // all even bits 0.
    static int changeEvenBits(int n)
    {
         
        // To store sum of bits
        // at even positions.
        int to_subtract = 0;
     
        // To store bits to shift
        int m = 0;
     
        // One by one put all even
        // bits to end
        for (int x = n; x > 0; x >>= 2)
        {
             
            // If current last bit
            // is set, add it to ans
            if ((x & 1) > 0)
            to_subtract += (1 << m);
     
            // Next shift position
            m += 2;
        }
     
        return n - to_subtract;
    }
     
    // Driver code
    public static void Main()
    {
        int n = 30;
         
        Console.Write(changeEvenBits(n));
    }
}
 
// This code is contributed by nitin mittal.

PHP




<?php
// PHP program to change even
// bits to 0.
 
// Returns modified number with
// all even bits 0.
function changeEvenBits($n)
{
     
    // To store sum of bits
    // at even positions.
    $to_subtract = 0;
 
    // To store bits to shift
    $m = 0;
 
    // One by one put all even
    // bits to end
    for ($x = $n; $x; $x >>= 2)
    {
         
        // If current last bit
        // is set, add it to ans
        if ($x & 1)
        $to_subtract += (1 << $m);
 
        // Next shift position
        $m += 2;
    }
 
    return $n - $to_subtract;
}
 
    // Driver code
    $n = 30;
    echo changeEvenBits($n) ;
 
// This code is contributed by nitin mittal
?>

Javascript




<script>
 
// js program to change even
// bits to 0.
 
// Returns modified number with
// all even bits 0.
function changeEvenBits(n)
{
     
    // To store sum of bits
    // at even positions.
    let to_subtract = 0;
 
    // To store bits to shift
    let m = 0;
 
    // One by one put all even
    // bits to end
    for (x = n; x; x >>= 2)
    {
         
        // If current last bit
        // is set, add it to ans
        if (x & 1)
        to_subtract += (1 << m);
 
        // Next shift position
        m += 2;
    }
 
    return n - to_subtract;
}
 
    // Driver code
    n = 30;
    document.write( changeEvenBits(n) );
 
// This code is contributed by sravan kumar
 
</script>

Output

10

Time Complexity – O(log n)

Space Complexity – O(1)

Method 2: (Bit masking)

C++




#include <bits/stdc++.h>
using namespace std;
 
int convertEvenBitToOne(int n) { return (n & 0xaaaaaaaa); }
 
int main()
{
    int n = 30;
    cout << convertEvenBitToOne(n);
    return 0;
}

Java




// Java program using Bitmask to
// Change all even bits in a
// number to 0
import java.io.*;
 
class GFG {
 
    static int convertEvenBitToOne(int n)
    {
        return (n & 0xaaaaaaaa);
    }
 
    // Driver code
    public static void main(String[] args)
    {
        int n = 30;
        System.out.println(convertEvenBitToOne(n));
    }
}
 
// This code is contributed by anuj_67.

Python3




def convertEvenBitToOne(n):
    return (n & 0xaaaaaaaa)
 
 
# Driver code
n = 30
print(convertEvenBitToOne(n))
 
# This code is contributed by Sachin Bisht

C#




// C# program using Bitmask to
// Change all even bits in a
// number to 0
using System;
 
class GFG {
 
    static long convertEvenBitToOne(int n)
    {
        return (n & 0xaaaaaaaa);
    }
 
    // Driver code
    public static void Main()
    {
        int n = 30;
        Console.WriteLine(convertEvenBitToOne(n));
    }
}
 
// This code is contributed by anuj_67.

PHP




<?php
// PHP program using Bitmask to
// Change all even bits in a
// number to 0
 
function convertEvenBitToOne($n)
{
    return ($n & 0xaaaaaaaa);
}
 
// Driver Code
$n = 30;
echo convertEvenBitToOne($n);
 
// This code is contributed by anuj_67.
?>

Javascript




<script>
 
// java script program using Bitmask to
// Change all even bits in a
// number to 0
 
function convertEvenBitToOne(n)
{
    return (n & 0xaaaaaaaa);
}
 
// Driver Code
n = 30;
document.write(convertEvenBitToOne(n));
// This code is contributed by sravan kumar
 
</script>

Output

10

Time Complexity – O(1)

Space Complexity – O(1)

This article is contributed by RISHABH RAJ JHA . If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
 


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