Maybe you were just trying to keep the sum_swap code clean and streamlined for ease of reading, but this method didn’t seem as air-tight as other example methods in the book. You may want to at least comment that not all cases are handled by the method.

Two ways I think this method might fail are 1) the method does not handle the case where swapping to even out the sums is not possible, and 2) since shift_amount is calculated with integer division and thus will always be an integer, I suspect that sum_swap could give an incorrect answer if sum_1 - sum_2 is an odd number.

Then again, maybe those types of caveats are understood and maybe I missed other such scenarios elsewhere in the book.

I’m getting close to the end…finally! Great book, very well-written and helpful for me!