Regex 正则表达式中的字符串替换

我试图用正则表达式替换字符串中的文本。我用c#完成了它，使用了相同的模式，但在swift中，它没有按照需要工作

这是我的密码：

var pattern = "\\d(\\()*[x]"

let oldString = "2x + 3 + x2 +2(x)"

let newString = oldString.stringByReplacingOccurrencesOfString(pattern, withString:"*" as String, options:NSStringCompareOptions.RegularExpressionSearch, range:nil)


print(newString)

更换后我想要的是：

“2*x+3+x2+2*（x）”

我得到的是：

“*+3+x2+*）”

试试这个：
(?
Try this:

(?<=\d)(?=x)|(?<=\d)(?=\()

This pattern matches not any characters in the given string, but zero width positions in between characters.

For example, (?<=\d)(?=x) This matches a position in between a digit and 'x'

(?<= is look behind assertion (?= is look ahead.

(?<=\d)(?=\()    This matches the position between a digit and '('

So the pattern before escaping:

(?<=\d)(?=x)|(?<=\d)(?=\()

Pattern, after escaping the parentheses and '\'

\(?<=\\d\)\(?=x\)|\(?<=\\d\)\(?=\\\(\)