as someone already mentioned, seeing only an example of the datafeed input would be useful.
It looks like each data line of the datafeed is a batch of invoices, and each invoice, which is separated by a semicolon, it is a series of columns separated by a comma. Each of these invoices has in the second column, its invoice number.
and then you work just with invoice number.
task 1) asks to compare each invoice number in within a batch, to that the a ascending order is respected.
task 2)asks to check if the invoices numbers are unfitting. which means what? different length? different datatype?
can you give some feedback on what i wrote? thanks.