[프로그래머스] 핸드폰가리기

func solution(_ phone_number:String) -> String {
    
    var arr:[String] = []
    var count = 0
    for i in phone_number.reversed() {
        if count <= 3 {
            arr.append(String(i))
        }else {
            arr.append("*")
        }
        count = count + 1
    }
    
    arr.reverse()
    
    
    
    return arr.joined()
}