wow

arent you copying acc over and over ?

you should be dooing the length check first if length is a mismatch not to go through a possibly huge iterator

this doesnt seem to work on a calculator

reason code does not work bouncing_ball is not defined anywhere however the test suite tries to use that function

what does firstNumber/first_number even mean ?

i think it would still be a better choise to do unwrap_or_default just to be safe

there's an issue with the random string tests somehow i think the random strings generated doesnt contain null at the end which results test to crash

i think you should't update the original string since this function returns a string