Consecutive Character Sequences

[Walter Brunswick]

Is there any way to [efficiently] iterate through a sequence of characters to find N [or more] consecutive equivalent characters?

So, for example, the string "taaypiqee88adbbba" would return 1 if the number (of consequtive characters) supplied in the parameters 
of the function call was 2 or 3, because "a", "e", 8, and "b" is repeated 2 or 3 times.

Thanks for any assistance.
W. Brunswick.