That your code is returning a string, see those quotes, instead of a number.

which means expected '0' to equal +0 ?

working now, actually you gave me the right direction to get into the problem, Thanks mate.

actually the same code working fine in vs code, dont know why here it is throwing error.

Your function does not return anything, does it?

This problem shouldn't have been in the fundamental category, although it is beginner level.

Did you add all necessary imports to your code?

why is my solution failing to pass because of Lists and ArrayList keywords, are they not allowed ?

shitty challenge

No! The kata is correct check your code.

your solution is approved already, but in next time mark your comment as a spoiler.