How do I check if a number string is in running sequence

Question

Is there a regex (or any other way) to check if a numbers in a string is in running sequence?

E.g.,

"123456" will return true
"456789" will return true
"345678" will return true
"123467" will return false
"901234" will return false

Answer 1

If all your sequences are composed of single-digit numbers, then you can solve this by observing that all correct sequences must be substrings of the longest such sequence, i.e. of "0123456789". So the check can be done like this:

bool res = "0123456789".Contains(str);

Demo on ideone.

Answer 2

How about this:

text.Skip(1).Zip(text, (c1, c0) => new { c1, c0 }).All(c => c.c1 - c.c0 == 1)