We have noticed couple of solutions with the same big O notation as accepted solutions not passing due to different compiler optimizations.
To fix this we decided to slightly increase time and memory limit constraints and regrade problems Arrow and Primitive Pythagorean Pairs.
Travelling Knight is also getting an update to slightly increase the diversity of possible approaches.
Updated time/memory constraints:
Arrow: 2s/256MB -> 4s/256MB
Primitive Pythagorean Pairs: 1s/128MB -> 2s/256MB
Travelling Knight: 0.5s/512MB -> 1s/512MB
Bubble Cup Crew