PHP programmer interview questions - written test part (Taobao company)

Please use php or other languages ​​to implement the following functions. PHP interview questions, please refer to the following: 1) 12 people of different heights are arranged in two rows, from small to large, with the front larger than the back. How many are arranged?

2) The format and method used by the open (file, mode, ...) function of the perl language. Can mode be omitted?

3) Usage of sed: How to make a.txt file that is a mixture of windows and unix formats into all unix formats

4) Given three numbers a, b, c, ask whether a*b=c is established in base 12 or base 18

5) On the 36th floor, the elevator can only stop on two floors. Users can only go to one of the floors and then climb down to the destination. Design an algorithm to minimize the total number of floors climbed by the user?

6) Collection record user_id, item_id; purchase record user_id, item_id; find out the users and goods that both collected and purchased. Each type of log is massive and cannot be put into memory at once? The above test questions also include perl and sed, so please pay attention.