[PRL] Re: [plt-internal] cisco router problem

[Matthias Felleisen]

No. "Stories" are better with students here and other regular places. 
Real stories that they can do on their own.

Naturally, at a place where everyone is brilliant you don't need 
stories to motivate performance problems you won't need this. Just 
showing them the history of algorithmics, starting with MIX
is enough.

-- Matthias


On Wednesday, January 14, 2004, at 04:06 PM, Shriram Krishnamurthi 
wrote:

> I suppose the entire history of algorithmics isn't enough as a source
> of examples? (-:
>
> Shriram
>
> Matthias Felleisen wrote:
>
>> Close. The reason I am pushing him is to get a cute little example for
>> 212 students. Here is something you can design.  Let's stress. Hah,
>> it's too slow, and it's not Java's fault. How can we do better?
>>
>> If we can find four or five more things like this, 212's O stuff
>> becomes more interesting and accessible to students.
>>
>> -- Matthias
>>
>>
>> On Wednesday, January 14, 2004, at 03:27 PM, Mitchell Wand wrote:
>>
>>> I'm assuming the following is a reasonable abstraction of the 
>>> problem:
>>>
>>> Given two long lists of integers (possibly with duplicates), one much
>>> longer than the other, find their intersection.
>>>
>>> Doing intersection (or DB join) is usually a n^2 problem.
>>>
>>> Some standard solutions:
>>>
>>> 1.  Read the big list once and the smaller list many times.  I'm
>>>     guessing he's already thought of this.
>>>
>>> 2.  Keep the lists sorted.  That way it turns into a O(n) problem.  
>>> If
>>>     you have to sort the lists, that makes it O(n log n).
>>>
>>> 3.  Preprocess the smaller list once to get a hashtable of possible
>>>     hits.  That way you only scan through the small list for big-list
>>>     elements
>>>
>>> 4.  Indices are Good Things. (Generalization of #3).
>>>
>>> --Mitch