Prime Factorization

In this lesson you will learn how to factor a number into primes in Swift, covering a number-theory algorithm built on loops. This is for anyone searching for "Swift prime factorization implementation".

Prime factorization means expressing a number as a product of primes. Try dividing by 2, then 3, and so on; whenever a divisor works, keep dividing by it.

The sample code starts at d = 2 and, for as long as num divides by d, records it with factors.append(d) and divides with num /= d. When it no longer divides, d increases by one, repeating until num reaches 1.

A common stumbling block for beginners is the nested loop structure. The outer loop raises the divisor d while the inner loop keeps dividing for as long as it can - grasp that two-stage combination and the whole algorithm falls into place.

It is an important idea spanning mathematics and computer science that underpins the security of cryptography such as RSA. Since 1 divides everything, it is excluded from prime factorization.

📖 Reference code

func primeFactors(_ n: Int) -> [Int] {
    var factors: [Int] = []
    var num = n
    var d = 2
    while num > 1 {
        while num % d == 0 {
            factors.append(d)
            num /= d
        }
        d += 1
    }
    return factors
}

print(primeFactors(60))
print(primeFactors(97))

✍️ Your code

Type your code, then press "Run"

🧪 This site can't compile or run Swift directly, so it checks on the spot whether what you typed matches the reference code (scoring happens entirely in your browser — nothing is sent anywhere).