Hi, I am having difficutlties with this CSES problem "Book Shop". Firstly I implemented it recursively, but it gave me TLE. (Link). I've also been trying to get into iterative dp, so I tried it too and it worked! (Link)
However, I don't understand why recursive approach doesn't pass. Maybe I have implemented it poorly?
Also, it seems that there is an approach with $$$O(x)$$$ space complexity, but I have no clue how it works.
It might be because recursive functions use up the call stack and that can get expensive enough to get a TLE.
Well, recently I've had a dilemma whether to use iterative approach, or a recursive one. Iterative seems to get an upper hand here. But there got to be a way for recursive approach to pass...
The issue is CSES. They have very strict time limits.