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 00000111Binary representation of b is 00001010 We need to flip highlighted three bits in a to make it b.

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.

Output :

4

Thanks to **Sahil Rajput** for providing above implementation.

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

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@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.