If you are having issues with this Kata, as I did, and don't know (yet) how to work with Regular Expressions, I would like to make you know that the examples in the Description might suggest a direction to solve this problem that it's not truly honest with you. The examples presented, don't alow you to think about a case where the string contains ONLY NUMBERS or a case where the left side is alphanumeric and the right side (wich is the most important, because the increment will be made through it), obviously, is entirely numeric.

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I'll give you an exemple.

string = './7r.145Q;'M0_105284850&668248?9600000000'

The alphanumeric side (or left side) of this string is './7r.145Q;'M0_105284850&668248?' and the numeric (or right) side is '9600000000'.

After doing the increment, the expected result is './7r.145Q;'M0_105284850&668248?9600000001', but ALL THE CASES TO CONSIDER showned in the Description are representations of a SINGLE CASE where the alphanumeric side is exclusively ALPHABETHIC (A-Z) and it is concatenated (or not) with the numeric side.

I think you will agree with me that the Description of this Kata is not very clear about some cases, wich is a problem.

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So, if you are still trying to solve this Kata without using Regular Expressions (it is possible, I did), think about what I said, think about these hidden cases.

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I hope this suggestion helps you and the others that are having issues with this Kata and I also hope to see this hidden cases issue solved, with more other possible cases presented in the Description.