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LINQ Ruined My Favorite Interview Question

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Re: LINQ Ruined My Favorite Interview Question

#101

Post by spenuke »

matchu wrote: post #78
spenuke wrote: post #68

Earlier quoted context omitted.

I'm a newbie, but the question seemed approachable so I went for it. This is what I came up with. (Python, btw.) def top_ten(s): words = s.split(' ') word_list = set(words) return sorted(word_list, key=lambda x: words.count(x))[:10] The question didn't ask for word counts, so I didn't see the need for a dictionary. I'd appreciate any advice on my solution. I'd be thrilled if I'm not too far off from being capable of…

The need for the dictionary shows up when your text gets significantly large. Each call to `words.count` is going to re-examine each word of the text to count 'em up, so, if n is the number of words in the text, and m is the number of distinct words in the text, then this solution is at least O(mn + n log(n)) whereas the dictionary-based solution is O(n log(n)). That is, we're re-reading the word list over and over,…

Hey, thanks much! I'm going to have to spend some time with these logarithmic evaluations to really get what you're saying, but I dig the basic concept. Very helpful.

Re: LINQ Ruined My Favorite Interview Question

#102

Post by recursive »

MatthewPhillips wrote: post #35
overgard wrote: post #4

LINQ tends to get thought of as "database syntax sugar", but it's way more than that. It's C#'s version of the lazy collection operations you find in most functional languages, just given friendlier sqlish names. (IE, "Select" instead of "map" and "Where" instead of "filter") I almost feel a bit gross when I have to write a "foreach" loop at this point, because there's almost always an equivalent way to do it in LINQ…

The most annoying thing about LINQ is that they use the SQL language. So unless you use C# and LINQ all of the time it's hard to figure out what functions translate to the ones used by every functional language in the world. I wish they would at least alias map, reduce, some, etc.

You really only have to figure it out once. And for users not familiar with the "standard" names, I think linq's naming is actually more intuitive.

Re: LINQ Ruined My Favorite Interview Question

#103

Post by calibraxis »

colanderman wrote: post #43
llambda wrote: post #8

I hate to be the bearer of bad news, but I think there may be even simpler solutions to this problem: (take 10 (reverse (sort-by (comp first rest) (frequencies (string/split ... #"\+s")))) The above is a Clojure one-liner example that I believe satisfies the original problem. So while LINQ may have simplified from the C-language family solutions he had seen, it's clearly possible to take it one step further with the…

expressivity of modern languages like Clojure Uh, no. Your solution just uses a bunch of standard library functions (at least, I hope they're not syntactic forms… and why a function as specific as "frequencies" not in some namespace boggles my mind). I could write that in C with an appropriate standard library. Ironically, expressing this in something like SQL actually speaks to the expressivity of the language becau…

`frequencies` is surprisingly useful, enough to justify its inclusion into core. I once pondered why.

Consider that in Clojure, a common act transforming one datastructure into another. Typically only a few kinds: maps, sets, and some kind of sequence.

What is a highly common generic transformation of a sequence to a map? `frequencies`. Particularly since you'd only be doing this with pretty finite sequences, given the finite nature of the built-in maps. Finite here means countable. What generic, domain-independent thing would you be counting? Often, the items themselves.

Re: LINQ Ruined My Favorite Interview Question

#104

Post by shill »

wiredfool wrote: post #97
shill wrote: post #31

Earlier quoted context omitted.

Without imports: d = {} for word in s1.split(' '): try: d[word] += 1 except KeyError: d[word] = 1 print [(x, d[x]) for x in sorted(d, key=d.get, reverse=True)][:10]

Or, use a defaultdict(int), or more in line with yours: d[word] = d.get(word,0) + 1 dictionary.get is quite useful. Also, I'd consider s.split(None), instead of s.split(' '). It will group whitespace, so that any double space or other whitespace is collapsed into one delimiter.

I didn't know about split(None). Thanks!

Re: LINQ Ruined My Favorite Interview Question

#105

Post by mzs »

llambda wrote: post #8

I hate to be the bearer of bad news, but I think there may be even simpler solutions to this problem: (take 10 (reverse (sort-by (comp first rest) (frequencies (string/split ... #"\+s")))) The above is a Clojure one-liner example that I believe satisfies the original problem. So while LINQ may have simplified from the C-language family solutions he had seen, it's clearly possible to take it one step further with the…

For a sys-admin job:

tr 'a-z' 'A-Z' | sed 's/[^A-Z][^A-Z]*/\ /g' | grep -v '^$' | sort | uniq -c | sort -nrk1 | head -10

edit: I don't know enough about HN,there should be a newline after the backslash in the sed command.

Re: LINQ Ruined My Favorite Interview Question

#106

Post by grannyg00se »

kephra wrote: post #7

/me wonders are candidates allowed to chose their favorite language? man bash | tr '[:upper:] ' '[:lower:]\n' | sed '/^$/d' | sort | uniq -c | sort -rn | head | awk '{ print $2 }' | fmt or do you only hire windows coders?

Awesome. I was going to post my two line javascript version, but instead I'm going to study this. There are three commands I've never heard of there. And it's definitely time to take a first crack at awk.

Re: LINQ Ruined My Favorite Interview Question

#107

Post by untog »

rhizome wrote: post #89
untog wrote: post #42

Earlier quoted context omitted.

I think the point still stands though, when you think of it as an interview question. The point is to get to the bottom of how the candidate would process such a query themselves, not to test their knowledge of the core libraries of their favourite language. I feel like that's what the post author meant when he said that LINQ had "ruined" the question- because it kind of does the same thing.

Isn't it kind of axiomatic that any question that provides for a concise and measurable solution will eventually be refactored into a library? It seems like kind of a weakness in these kinds of "programmer" questions, that they all regress to trivia. Why not an open-ended business problem and/or deliverables-type question? I'm sure that would speak more to the daily job, where I've never heard of someone being tasked…

Surely the 'trivia' in this instance is knowing the names of libraries, as opposed to be able to think through programming concepts?

Just like math homework back in the day, the teacher didn't do it to check your answer, they did it to check how you arrived at your answer.

Re: LINQ Ruined My Favorite Interview Question

#108

Post by Strilanc »

corresation wrote: post #91
Strilanc wrote: post #75

Earlier quoted context omitted.

Functional languages use the concepts you're criticizing even more extensively than LINQ does.

What are the "concepts I'm criticizing"? I suspect that you have absolutely no idea what the context of my comment was, because your diversion on the topic of functional programming is just grossly out of place. LINQ encourages the belief that set operations are free , such that you no longer have to concern yourself with concepts like memoization or appropriate structures. This has nothing to do with functional prog…

You've actually been pretty vague about the concepts you're criticizing, except for "LINQ". Now I can see you were alluding to just the deferred execution part (the "lack of memoization").

Basically, you're saying it's too easy to accidentally perform a computation twice by iterating through a sequence twice. Recurse on that problem and you get an exponential blowup.

That is actually a problem mostly unique to LINQ and it is really important that a programmer understand the deferred semantics. Some tools, e.g. ReSharper, will detect multiple enumerations and warn you about it. Judicious use of ToArray/ToList solves most issues with defer-splosion.

Re: LINQ Ruined My Favorite Interview Question

#109

Post by gecko »

tolmasky wrote: post #98

My main problem with LINQ is that it seems to perform terribly on mobile. I was looking for map/reduce/etc type functions for C# in Unity, and thought I found it with LINQ. To my dismay, LINQ creates so many crazy intermediate objects to pull off its "laziness" that our GC high water mark was being crossed all the time. I went and just reimplemented everything from underscore.js in C# and got way better performance.…

It's not mobile; it's old versions of Mono having a completely shit GC. Do you know whether Unity has upgraded to SGEN yet?

Re: LINQ Ruined My Favorite Interview Question

#110

Post by anonymous »

kephra wrote: post #7

/me wonders are candidates allowed to chose their favorite language? man bash | tr '[:upper:] ' '[:lower:]\n' | sed '/^$/d' | sort | uniq -c | sort -rn | head | awk '{ print $2 }' | fmt or do you only hire windows coders?

You don't need that tr, just sort -f and then uniq -i. Of course, whoever put -f as the ignore-case flag for sort should be shot methinks, or rather the one who first added -i as "ignore nonprinting characters".

Edit: and while we're on the subject, you can get rid of head and use awk 'NREdit²: I would also like to point out that your version is superior to any short C# program, because sort can sort sequences that exceed the amount of RAM you have.

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