Question

How to check whether a number is a perfect number in Swift

Answer 1

// If the sum of all factors of a number is equal to the number, then the number is perfect
 
// Factors of a number are numbers that divide the number evenly
    
// 6
// factors = 1, 2, 3
// 1 + 2 + 3 = 6

import Foundation

let num = 6
var sumOfFactors = 0

for i in 1..<num {
    if num % i == 0 {
        sumOfFactors += i
    }
}

if sumOfFactors == num {
    print("Perfect Number")
} else {
    print("Not a Perfect Number")
}



/*
run:

Perfect Number

*/

 

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Answer 2

// If the sum of all factors of a number is equal to the number, then the number is perfect
 
// Factors of a number are numbers that divide the number evenly
    
// 6
// factors = 1, 2, 3
// 1 + 2 + 3 = 6

import Foundation

func isPerfect(_ n: Int) -> Bool {
    if n < 2 { return false }

    var sum = 1
    let limit = Int(Double(n).squareRoot())

    if limit >= 2 {
        for i in 2...limit {
            if n % i == 0 {
                sum += i
                let pair = n / i
                if pair != i { sum += pair }
            }
        }
    }

    return sum == n
}

func main() {
    print("Perfect numbers up to 10,000:")
    for i in 1...10000 {
        if isPerfect(i) {
            print(i)
        }
    }
}

main()


/*
run:

Perfect numbers up to 10,000:
6
28
496
8128

*/

 

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