Digit DP - Devu and Locks misplaced

[Oz121]

In the Digit DP module, the problem Devu and Locks seems to be too hard/requires advanced topics. The official editorial here: https://discuss.codechef.com/t/devlock-editorial/9727 uses FFT and Matrix Exponentiation. There are also no user solutions posted on usaco guide, so others probably found it too complex.

I believe this has been mentioned before: https://forum.usaco.guide/t/devu-and-locks/5195, which probably explains the issue a lot better than I can.