Saturday, September 8, 2007

google-style interviews: apply comp-science principles to real problems

Hi LS,

Now I think yesterday's toughest interview questions are similar in spirit to Google interview questions. I think the key skill tested yesterday was "how does this candidate apply computer science constructs to real world problems". That's what I meant when I said "connecting the algorithms/data-structures with the given requirements". Before you can identify any algo/data-structure to model the requirements, you have no clue how to support the requirements. Whenever we see a first-in-first-out system like Green Card applicants, we automatically think of a Queue data structure -- ie connecting the Queue construct to a real world problem.

A 6-year veteran developer like me is supposed to be familiar with
1) associative arrays, hashmaps, sets, binary search trees, doubly linked lists, multi-dimensional arrays and (hopefully) circular linked lists, binary heaps, red-black trees, and any combination of the above like a stack of hashmaps,

2) the concepts of space efficiency, time efficiency, random access, sequential access, what can/can't be sorted ...

4) OO design patterns
3) OO concepts of dependency, coupling, polymorphism, static, multiple inheritance, HAS-A vs IS-A, setters (extremely important) ...

But this veteran may not know how to APPLY these constructs to a real-world problem, according to my observation. All of Google's and my recent problem-solving interview questions attempt to test a candidate's analysis skill to "apply tools to problems". In my case, I couldn't applied the Strategy design pattern unless I spot the similarity between the given requirement and the Strategy pattern's requirements.

The 4 groups of tools mentioned above are simple tools when studied individually, but any design that need tools from 3 of these groups is likely to be non-trivial. Consider algorithms to delete a node from a binary search tree.

Finally I have some idea why Google like those questions, including the question about "1-7 random number generator using a 1-5 generator".

1 comment:

Mobile Weather system said...

Before you can identify any algo/data-structure to model the requirements, you have no clue how to support the requirements. Whenever we see a first-in-first-out system like Green Card applicants, we automatically think of a Queue data structure

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