[프로그래머스]문자열 다루기 기본(Swift)

func solution(_ s:String) -> Bool {
    
     let chars = Array(s)
    
     guard chars.count == 4 || chars.count == 6 else { return false }
    
     for c in chars {
         if c.isLetter {
             return false
         }
     }
     return true    
}

func solution(_ s:String) -> Bool {    
    return (Int(s) != nil && (s.count == 4 || s.count == 6)) ? true : false
}