8. String to Integer (atoi) (Medium) (Microsoft, Amazon, Uber, Bloomberg) +Google

Implement atoi to convert a string to an integer.

Hint: Carefully consider all possible input cases. If you want a challenge, please do not see below and ask yourself what are the possible input cases.

Notes: It is intended for this problem to be specified vaguely (ie, no given input specs). You are responsible to gather all the input requirements up front.

Update (2015-02-10):
The signature of theC++function had been updated. If you still see your function signature accepts aconst char *argument, please click the reload buttonto reset your code definition.

spoilers alert... click to show requirements for atoi.

Follow up 1(Google):

之后问怎么test，找了各种诡异的string来test我。有些corner cases