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.

// Count number of bits to be flipped // to covert 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; }

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

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