Chewbacca and Number problem

#1

I really don’t understand, what does this problem want to say. please provide more test input and output cases with clarification.

#2

It’s a fairly complete explanation in itself. Anyways, imagine you have a number like 789056, then you can replace each digit with (9 - that digit). Your aim is to make this number the smallest possible using any number of such operations. Now, for this case, you can invert digit 7 to 2, 8 to 1, 9 to 0, NOT 0 to 9, 5 to 4, and 6 to 3 so that the final number you get is 210043.

#3

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