Riverside <3

do vector addition on int[] arrays (...) using the + operator

Your solution is incomplete (and the error message comes from it not fulfilling the requirements).

weird, for me it works in 1100ms, 10 times faster than the limit.

• mutating the input is a very bad practice. You'll pass the tests even doing so, now, but if you keep that habit, your future colleagues will hate you... x)
• if you time out with this algo, that means you didn't implement it correctly (it passes the tests, otherwise).

don't mutate the input array

:-)

It is not a regex character, but the part of the %s, string represention, which is the old string formating style in python.
So, here the content of all_leap_year is placed where %s is at.