Question

How to write 4 different functions that check if a number is a power of 2 in Scala

Answer 1

object PowerOfTwoCheck {

  // Method A: Bit‑counting
  def isPowerOfTwoA(x: Int): Boolean = {
    if (x <= 0) false
    else x.toBinaryString.count(_ == '1') == 1
  }

  // Method B: Bitwise trick
  def isPowerOfTwoB(x: Int): Boolean =
    x > 0 && (x & (x - 1)) == 0

  // Method C: Repeated division
  def isPowerOfTwoC(x: Int): Boolean = {
    if (x <= 0) return false
    var n = x
    while (n % 2 == 0) {
      n /= 2
    }
    n == 1
  }

  // Method D: Using logarithms
  def isPowerOfTwoD(x: Int): Boolean = {
    if (x <= 0) false
    else {
      val logv = math.log(x) / math.log(2)
      math.abs(logv - logv.round) < 1e-10
    }
  }

  def main(args: Array[String]): Unit = {
    val test1 = 16 // true
    val test2 = 18 // false

    println(s"A: ${isPowerOfTwoA(test1)}, ${isPowerOfTwoA(test2)}")
    println(s"B: ${isPowerOfTwoB(test1)}, ${isPowerOfTwoB(test2)}")
    println(s"C: ${isPowerOfTwoC(test1)}, ${isPowerOfTwoC(test2)}")
    println(s"D: ${isPowerOfTwoD(test1)}, ${isPowerOfTwoD(test2)}")
  }
}



/*
OUTPUT:

A: true, false
B: true, false
C: true, false
D: true, false

*/

 

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