在swift中将字符串转换为邮政编码格式

import Foundation

func formatPostalCode(_ input: String) -> String {
    let pattern = "^(\\d{6})$"
    let replacement = "$1"
    
    if let regex = try? NSRegularExpression(pattern: pattern, options: .anchorsMatchLines) {
        let range = NSRange(location: 0, length: input.utf16.count)
        let formattedString = regex.stringByReplacingMatches(in: input, options: [], range: range, withTemplate: replacement)
        return formattedString
    }
    
    return input
}

let inputString = "123456"
let formattedString = formatPostalCode(inputString)
print(formattedString) // 输出：123456