All very good answers. many thanks for you guys,
In a word, the Liner Search is the cheapest method to search. the
other two are complicated and expensive.

I know it is about algorithmic complexity, but I totally forget the
defination of the O, even the Log. University time seems a century ago
I almost forget everything.

I think it is useless for 99% programmer jobs, unfortunately it's
always been asked. Once a interviewer asked me to explain the
algorithmic complexity of quick sort!


Thanks again