i'll try do my best

IMHO. Code Style is not good

It checks if a number is even. Just an alternative way of saying n % 2 == 0

(n&1) == 0. What is this line doing?

Thank you for your reviewing.

Should check for null though.

Misunderstood circle. Thought it could go two ways.

Wrong if statement. Should be (n < 0 || (n & 1) == 0)

There is a solution that will not time out. I'll make a note on the description. Thanks for the feedback.

Yes, I have missed that case. Thank you for comment.

should note that:
1.return -1 if n<1
2.control the time

I think this is an interesting problem as it's so simple in theory, and the solutions can be really elegant.

Agree completely!