Mandrake You are absolutely correct, but OP has not given enough samples of input and he has not given the exact requirement clearly, which I mentioned in my first reply itself and the samething was highlighted by ikegami and chargrill. So I assumed he might have inputs with incremented characters inbetween instead of random characters.

ikegami has mentioned

We can't help you if you can't even describe what you want accuratly

chargrill has mentioned

I don't know what you mean. Solid examples will speak volumes, show us what output you want to get.