Count number of bits to be flipped to convert A to B

Given two numbers ‘a’ and b’. Write a program to count number of bits needed to be flipped to convert ‘a’ to ‘b’.

Example :

Input : a = 10, b = 20
Output : 4
Binary representation of a is 00001010
Binary representation of b is 00010100
We need to flip highlighted four bits in a
to make it b.

Input : a = 7, b = 10
Output : 3
Binary representation of a is 00000111
Binary representation of b is 00001010
We need to flip highlighted three bits in a
to make it b.

Recommended: Please solve it on “PRACTICE” first, before moving on to the solution.

  1. Calculate XOR of A and B.      
        a_xor_b = A ^ B
  2. Count the set bits in the above 
     calculated XOR result.
        countSetBits(a_xor_b)

XOR of two number will have set bits only at those places where A differs from B.

C++

// Count number of bits to be flipped 
// to convert A into B 
#include <iostream> 
using namespace std; 
  
// Function that count set bits 
int countSetBits(int n) 
{ 
    int count = 0; 
    while (n) 
    { 
        count += n & 1; 
        n >>= 1; 
    } 
    return count; 
} 
  
// Function that return count of 
// flipped number 
int FlippedCount(int a, int b) 
{ 
    // Return count of set bits in 
    // a XOR b 
    return countSetBits(a^b); 
} 
  
// Driver code 
int main() 
{ 
    int a = 10; 
    int b = 20; 
    cout << FlippedCount(a, b)<<endl; 
    return 0; 
} 

Java

// Count number of bits to be flipped 
// to convert A into B 
import java.util.*; 
  
class Count { 
      
    // Function that count set bits 
    public static int countSetBits(int n) 
    { 
        int count = 0; 
        while (n != 0) { 
            count += n & 1; 
            n >>= 1; 
        } 
        return count; 
    } 
  
    // Function that return count of 
    // flipped number 
    public static int FlippedCount(int a, int b) 
    { 
        // Return count of set bits in 
        // a XOR b 
        return countSetBits(a ^ b); 
    } 
      
    // Driver code 
    public static void main(String[] args) 
    { 
        int a = 10; 
        int b = 20; 
        System.out.print(FlippedCount(a, b)); 
    } 
} 
  
// This code is contributed by rishabh_jain 

Python3

# Count number of bits to be flipped 
# to convert A into B 
  
# Function that count set bits 
def countSetBits( n ): 
    count = 0
    while n: 
        count += n & 1
        n >>= 1
    return count 
      
# Function that return count of 
# flipped number 
def FlippedCount(a , b): 
  
    # Return count of set bits in 
    # a XOR b 
    return countSetBits(a^b) 
  
# Driver code 
a = 10
b = 20
print(FlippedCount(a, b)) 
  
# This code is contributed by "Sharad_Bhardwaj". 

C#

// Count number of bits to be 
// flipped to convert A into B 
using System; 
  
class Count { 
      
    // Function that count set bits 
    public static int countSetBits(int n) 
    { 
        int count = 0; 
        while (n != 0) { 
            count += n & 1; 
            n >>= 1; 
        } 
        return count; 
    } 
  
    // Function that return 
    // count of flipped number 
    public static int FlippedCount(int a, int b) 
    { 
    // Return count of set  
    // bits in a XOR b 
        return countSetBits(a ^ b); 
    } 
      
    // Driver code 
    public static void Main() 
    { 
        int a = 10; 
        int b = 20; 
        Console.WriteLine(FlippedCount(a, b)); 
    } 
} 
  
// This code is contributed by vt_m. 

PHP

<?php 
// Count number of bits to be  
// flipped to convert A into B 
  
// Function that count set bits 
function countSetBits($n) 
{ 
    $count = 0; 
    while($n) 
    { 
        $count += $n & 1; 
        $n >>= 1; 
    } 
    return $count; 
} 
      
// Function that return  
// count of flipped number 
function FlippedCount($a, $b) 
{ 
    // Return count of set  
    // bits in a XOR b 
    return countSetBits($a ^ $b); 
} 
  
// Driver code 
$a = 10; 
$b = 20; 
echo FlippedCount($a, $b); 
  
// This code is contributed by mits 
?> 

Output :

Thanks to Sahil Rajput for providing above implementation.

To get the set bit count please see this post: Count set bits in an integer

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