.

You're misunderstanding what a rotation is if you say there are 23 of them. Have you read the wikipedia link?

There are 23 rotations of string 'bsjq'. Array ["bsjq", "qbsj", "sjqb", "twZNsslC", "jqbs"], wich contain only 5 elements can't include all 23 rotations. I can't anderstand why this case return true.

Check my code for a more optimized version of your def get_sum

Ah should have looked at the test cases a bit more thoroughly. Thank you

Which is smaller?

29917 or 201997
26945 or 209645

Yes of course you need to know the color of the field :D 1 is black and 0 is white.

In the example QRCode, it goes from black -> black -> white..
Also, dont you need to know the color of the field to determine if it will be a 0 or 1? If field is black and x+y%2 is 0 -> add 0. If not, add 1. z

I took a example QRCode. The field will be always different, you only have to understand the way you go through the field. (Like the red arrow)

Hello, can someone help me understand the question a bit better..

We start with the first pixel (in the lower right corner, where also the red arrow begins) which is black, but we have to use mask because (20+20)%2 is 0, therefore we don't add 1 to our bit sequence but 0.
Next field is white. This time we don't use mask because (20+19)%2 isn't 0, so we add a 0 to our bit sequence.
Next field is black. This time we don't use mask because (19+20)%2 isn't 0, so we add a 1 to our bit sequence.

How do you know if the field is white or black?

The init in all som cases are set to the number 0

Right, no problem with that. The parameter init is what it is. Nobody said it should be a[0].