I think he just interprets three spaces as two spaces that will become one, and one space that will become nothing.

seems like you have an extra whitespace character at the end of your output

sorry, I'm blurred, why $res has to be start at 1, and why you can convert this [1! + 2! .... n!] to only 1...
Is it a math theory or....?

It's alright now, I finally solved it. Thanks

Hi. Please say which language you are using. Also, please use markdown tags to format codes or logs, or it may be unusable (see there: https://docs.codewars.com/training/troubleshooting/#post-discourse ). For example, trailing or consecutive spaces don't display properly, but it seems your answer contains an extra trailing space.

I passed the first two cases but failed in the last case. It said
"
Failed asserting that two strings are equal.
Expected: 'E'
Actual : 'E '
"
But when I try it with hardcode, it came out with the expected answer, but I'm keep getting wrong when attempt...
Help...