I don't understand 16-5 solution

[StromanStroman]

I have read the solution a but I do not quite understand the accurate meaning of the content.
So would you please give me a pseudocode to make me clear?

for example
you said 'starting with the elements in an arbitrary order, process the sequence h r1, . . . , rni from right to left'.You mean I must deal with it from right to left?If that why does arbitrary order here?

you said 'make a note'.What note would you like me to make?It is a word that difficult to understand.

I don't understand the description of b,c for I don't understand a.