c# validate that string contains matching number of brackets

Question

If I have a string like this...

"123[1-5]553[4-52]63244[19-44]"

...what's the best way to validate the following conditions:

1. Every open bracket has a matching close bracket
2. There are no more than 3 sets of brackets
3. There are no nested brackets (i.e., [123-[4]9])

Would a regex be able to validate all of these scenarios? If not, how about LINQ?

Answer 1

Because you don't allow nesting, you can use a regex:

^([^[\]]*\[[^[\]]*\]){0,3}[^[\]]*$

Explanation:

• (...){0,3} matches up to three sets of the following:
  • [^[\]]* matches optional non-bracket characters
  • \[ matches [ to open a group
  • [^[\]]* matches optional non-bracket characters inside the group
  • \] matches ] to close the group
• Finally, [^[\]]* matches more optional non-bracket characters after all of the groups