I was practicing an old problem 757G and I met a huge speed difference among different c++ standard.

I received TLE (> 5000ms) when submitting with c++17 (64, win). But the exact same code do run fast (< 800ms) in the corresponding testcase when submitting with c++17 or c++20 (64, win).

I'm wondering why this could happen. I will be graceful if kindly everybody could point out the reason.