Question

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

Answer 1

import Foundation

// Method A: Bit‑counting
func isPowerOfTwoA(_ x: Int) -> Bool {
    if x <= 0 { return false }
    return x.nonzeroBitCount == 1
}

// Method B: Bitwise trick
func isPowerOfTwoB(_ x: Int) -> Bool {
    return x > 0 && (x & (x - 1)) == 0
}

// Method C: Repeated division
func isPowerOfTwoC(_ x: Int) -> Bool {
    if x <= 0 { return false }
    var n = x
    while n % 2 == 0 {
        n /= 2
    }
    return n == 1
}

// Method D: Using logarithms
func isPowerOfTwoD(_ x: Int) -> Bool {
    if x <= 0 { return false }
    let logv = log2(Double(x))
    return abs(logv - round(logv)) < 1e-10
}

let test1 = 16 // true
let test2 = 18 // false

print("A: \(isPowerOfTwoA(test1)), \(isPowerOfTwoA(test2))")
print("B: \(isPowerOfTwoB(test1)), \(isPowerOfTwoB(test2))")
print("C: \(isPowerOfTwoC(test1)), \(isPowerOfTwoC(test2))")
print("D: \(isPowerOfTwoD(test1)), \(isPowerOfTwoD(test2))")


/*
OUTPUT:

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

*/

 

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