regexp - find numbers in a string in any order

Question

I need to find a regexp that allows me to find strings in which i have all the required numbers but only once.

For example:

a <- c(\"12\",\"13\",\         


        

Answer 1

you can as well use this

grep('^([123])((?!\\1)\\d)(?!\\2|\\1)\\d', a, value=TRUE, perl=T)

see demo