Finding consecutive values

Question

Hi,
I want to find some 2 consecutive values on a table. Sample is like below. For example I want to find the index vales of "a" or "b".

Column1
a
b
c
d
e
f
a
b
c
f
a
b

How should be the logic?

I want to add all column's value to a datatable or an array? How should be the code, or loops?

regards.