Opposite result of a regular expression

Question

I have this regex

^(\d+)/\1$

that matches strings like

1/1
2/2
5/5

I want to get the inverse result of this regex. I browsed the net and stack overflow and found that

^((?!(\d+)/\1.).)*$

should do the trick, but it doesn't.

Could anyone point me into the right direction?

Answer 1

/^(\d+)\/(?!\1$)\d+$/

This will match 2/3 or 1/10, but not 1/1 and 2/2, et cetera. In other words, it will match only when the first part of the fraction is different from the second part.