The offset state is $S^{x_0}$ applied to the offset-zero periodic state. Part (b) therefore makes its QFT output distribution independent of $x_0$. Explicitly, only outcomes divisible by $A=N/r$ occur, each with probability $1/r$; $x_0$ contributes only a phase.


Solution

Past exam of the mathematics course of the University of Cambridge / 2021 / ii / Paper 4 / 10D / c / Solution

 Solution (source code)