Count the number of bit to be flipped to Convert A to B in Kotlin

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To count the number of bits to be flipped to convert A to B using bit manipulation, you can perform the following steps:

  1. XOR A and B to get a number C that has a 1 in each bit position where A and B differ and a 0 in each bit position where they are the same.
  2. Count the number of 1’s in C by performing a bit-count operation. There are various ways to do this, but one common method is to use a lookup table that has the number of set bits for each possible 8-bit value, and then combine the counts for each 8-bit chunk of C using bitwise operations.
  3. The resulting count is the number of bits that need to be flipped to convert A to B.
Kotlin
fun countBitsToFlip(a: Int, b: Int): Int {
    var c = a xor b
    var count = 0
    while (c != 0) {
        count += c and 1
        c = c shr 1
    }
    return count
}

fun main() {
    val a = 10 // 1010 in binary
    val b = 15 // 1111 in binary
    val bitsToFlip = countBitsToFlip(a, b)
    println("To convert $a to $b, we need to flip $bitsToFlip bits.")
}

In this implementation, we define a function called countBitsToFlip that takes two integers a and b as input and returns the number of bits that need to be flipped to convert a to b.

The function first computes the bitwise XOR of a and b to get a number c that has a 1 in each bit position where a and b differ and a 0 in each bit position where they are the same.

The function then initializes a counter variable count to 0 and enters a loop that continues as long as c is non-zero. In each iteration of the loop, the function checks whether the least significant bit of c is 1 by performing a bitwise AND with the value 1. If the result is 1, the function increments count. The function then shifts c one bit to the right using the shr operator to check the next bit.

After the loop completes, the function returns the value of count, which is the number of bits that need to be flipped to convert a to b.

Finally, we test the function by calling it with two example inputs and printing the result. The output should be “To convert 10 to 15, we need to flip 2 bits.”

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