[프로그래머스]숫자 변환하기(Swift)

import Foundation

func solution(_ x:Int, _ y:Int, _ n:Int) -> Int {
    var set: Set<Int> = [x]
    var count: Int = 0
    
    while !set.isEmpty {
        if set.contains(y) {
           return count
        }
        var nextSet: Set<Int> = []
        for e in set {
            if e + n <= y {
                nextSet.insert(e+n)
            }
            
            if e * 2 <= y {
                nextSet.insert(e*2)
            }
            
            if e * 3 <= y {
                nextSet.insert(e*3)
            }
        }
        set = nextSet
        count += 1
    }
    return -1
}