Because it's fun :)

Inspired by SecondThread's comment above, I thought I'd see how hard it would be to solve a Meta Hacker Cup problem at compile time. I chose to start with Round 2 A1, since the input is quite small. This is probably trivial since C++20 and above allow you to allocate memory in constexpr functions, so I gave it a whirl using C++17. This means no allocations are allowed, but the input/output parsing is luckily very straightforward for this problem.

The code is a bit long (118 lines), so I've included it in the link below. It appears to work on the three major compilers: https://godbolt.org/z/cYG1rTfWr.

Note that the compiled binary returns a random value, To actually view the answer, you can view the compiled binary in a hex editor, or do what I did:

$ strings a.out | grep Case
Case #1: 1
Case #2: 4
Case #3: 10
Case #4: 1
Case #5: 1
Case #6: 0

This code is also sufficient to pass the full data set (136 cases) without running into the default constexpr-ops limit. On my 2,3GHz Intel i5 laptop CPU from 2018, clang compiles the full data set in .5 seconds.

Does anyone know a nicer way of ensuring that ANS is not discarded by the compiler for not being used?