Golang regex extract from match

I need to use regex to extract and replace some text.

Any word that has the following needs to be replaced:

• sub-19 -> u19
• sub19 -> u19
• (sub19) -> u19

I have the following but it's missing one of the requirements and can't figure it out 100%

(?i)sub(?:[^a-z|0-9])

You can match non whitespace chars before and after and replace with group 1

(?i)\S*sub-?(\d+)\S*

See a regex demo

Example

package main
import (
    "regexp"
    "fmt"
)
func main(){
	var re = regexp.MustCompile(`(?i)\S*sub-?(\d+)\S*`)
    var str = `sub-19
sub19
(sub19)`
    
    fmt.Println(re.ReplaceAllString(str, "u$1"))
}

Output

u19
u19
u19

<hr>

If you don't want to remove leading and trailing non whitespace chars, you can omit the \S* and add a word boundary \b

(?i)\bsub-?(\d+)\b

See another regex demo