This might be frivolous question, so please have understanding for my poor soul.
After reading this article about Intelligent Design sort (http://www.dangermouse.net/esoteric/intelligentdesignsort.html) which is in no way made to be serious in any way, I started wondering whether this could be possible.
An excerpt from article says:
The probability of the original input list being in the exact order it's in is 1/(n!). There is such a small likelihood of this that it's clearly absurd to say that this happened by chance, so it must have been consciously put in that order by an intelligent Sorter.
Let's for a second forget about intelligent Sorter, and think about possibility that random occurrences of members in array are in some way sorted. Our algorithm should determine the pattern without changing array's structure.
Is there any way to do this? Speed is not a requirement.
The implementation is very easy actually. The entire point of the article is that you don't actually sort anything. In other words, a correct implementation is a simple NOP. As my preferred language is Java, I'll show a simple in-place implementation in Java as a lambda function:
list->{}
Funny article, I had a good laugh.
If the only thing you're interested in is that whether your List is sorted, then you could simply keep an internal sorted flag (defaulted to true for an empty list) and override your add() method to check if the element you're adding fits the ordering of the List - that is, compare it to the adjacent elements and setting the sorted flag appropriately.
When we converting from nfa to dfa there may be result like the image below... My question is, is it necessary to write that from state {4} it's going to Zero state? I mean that without showing the input symbol 1 of {4} is the same with picture below right? or no?
It’s a matter of convention. Personally, I prefer not to clutter my DFA with unnecessary states, especially since DFAs obtained via transformation from NFAs tend to become quite complex anyway, and since it’s deterministic we know that any non-displayed transition must be invalid.
However, I’ve experienced that many people in academia teach / use the other convention, and require all transitions to be explicitly shown. When working as a TA (tutor) I’ve actually had a discussion with a professor about this – he wanted us tutors to deduct points on the final tests for missing transitions in DFAs but I convinced him that deducting points for this was unfair.
it is not necessary to write {4}-> 0 transition because the automat is already accepting the word. this transition means only that this is "nothing" meaningful for our solution. but for details, it is useful to give it, to show the whole automaton.
It matters only if you are trying to draw the MinimalFA (MFA).
Actually you can generate infinite number of DFA s from a single NFA, each of which differ in number of states.
If you remove 'Dead States' in the figure,you will get the MFA.
The figure is OK if you just want a DFA
I have been asked in an interview how one can return more than one value from function. I have answered saying by using pointers we can achieve(call by reference) this in C. Then he told me he is looking for some other way of returning more than one value. I said we can return a struct object but here also he didn't seem to be impressed.
I would like to know others ways to return more than one value from a function.
I have seen this questions being asked here on SO, but could not find anything C specific.
The tricky problem is that the interviewer has some solution they are particularly happy with in mind and they are likely grading you by whether you have the same clever trick as them or not.
You could just name a few ways such as you did, and still not fall upon their secret trick. And if you knew their secret trick, you could well not be impressed with it.
So in these situations, its to turn it from interview into conversation. Once you detect you're not moving towards their ego, you can avoid heading towards the intimidating "I don't know" "I give up" and instead try out the "so do you have any clever solution? Is there an in-house recipe for this at Xyz Inc?" etc.
Any glimpse at their obviously self-impressed solution and you are back on firm ground where you can talk about it and ask them if they have thought about various factors that come to mind and basically interview them.
Everyone loves a good listener, and getting them to talk about their tricks is a good way to get them to leave the interview throughly impressed with you! ;)
There are a few ways:
Return value using the return statement (as you already know)
Return via references.
Return values via the heap.
Return values via global variables.
That depends on what you consider a value. If a value is a piece of information for you, more values could be a struct of values. More values could be also passed via pointers or arrays, even a char* containing a list of (non-zero alphanumerical) values. If you consider a value to be a bit of information a single returned uint32_t may hold 32 values. You could even mess around with signals or sockets or pipes or files.
But for you do not even know the use case and the requirements it imposes on the solution, it's indeed a rather hard task to come up with the right solution (and you actually did come up with some proper solutions ...).
Return a pointer to a structure, or pack several small datatypes into one large datatype, or use global variables.
The first is probably the cleanest way to do it, the other two might have their uses in certain situations.
If we pass the address instead of the true value of the parameters.
Then whenever we refer those parameters we do it with the address.
returning a pointer to structure is the suitable answer.(Obviously, the objective of the program can decide what's the best that can be done). The interviewer might have wanted you to say 'I don't know' which would have shown your lack of confidence in the field. I think you provided good solutions, though not what he had in his mind. You could have asked him about a typical scenario where he wanted multiple values to be returned and then discuss how struct-pointer is a reasonable alternative.
I'll be writing the online Google test tomorrow as a fresher. Apparently, they definitely ask one problem on Dynamic Programming?
Does anyone know of a good resource for collection of DP problems in C along with solutions? I know what DP is & have used it on an occasion or twice. However I feel to crack a DP problem in test, prior practice of typical problems will make it easier to approach.
Any good resources or problem sets with solutions in C will be highly appreciated. Thanks.
Okay, so I really hope this doesn't count as "shameless self-promotion," since all of these links are to code snippets I've posted on my personal site. If this is inappropriate, please let me know and I can take them down.
Here are a few fun DP problems that are pretty much classics:
Minimum edit distance: Given two strings A and B, find the shortest number of edits (insertions, deletions, or substitutions) necessary to convert A into B. This is called the Levenshtein distance. (My solution)
Optimal sequence alignment: Given two strings A and B, find the minimum number of gaps that must be inserted into the sequence to align A and B. This is called the Needleman-Wunsch algorithm. (My solution)
Single-source shortest paths: Given a directed graph G and a single node s, find the lengths of the shortest paths from s to each other node in the graph, assuming edges can be positive or negative but that no cycles exist. This is the Bellman-Ford algorithm. (My solution)
All-pairs shortest paths: Given a directed graph G, find the minimum distances between all pairs of nodes. This is the Floyd-Warshall algorithm. (My solution)
Hopefully this is somewhat useful, and best of luck tomorrow!
The Topcoder website is amazing. Not all of the problems use DP, but many do. Free full access to all problems from past competitions, which are at 3 different difficulty levels, as well as after-match explanations of every single problem from the problem author. Not only that, but you can quickly dig up the source code solution submitted by any coder in the competition.
Haven't been back there for a while, but they allow at least C++, Java, C# and I believe several other languages now.
I suggest u,collect a book "An Introduction to Bioinformatics Algorithms".This has a chapter fully on DP.As #templatetypedef mentioned Minimum edit distance,Optimal sequence alignment it has other problem with them.Though there is no implementation in it.You have to do it on your own.But you will find pretty interesting reading them.
To practice you can take one of the available problems at SPOJ. To recognize DP ones easily you can check at Problems Classifier (keyword: dp).
Recently I tried to explain some poorly designed code to my project manager. All of the manager classes are singletons ("and that's why I can't easily change this") and the code uses event dispatching everywhere that a function call would have sufficed ("and that's why it's so hard to debug"). Sadly it just came out as a fumbling mess of English.
Whats the most difficult thing you've had to convey to a non-technical person as a programmer? Did you find any analogies or ways of explaining that made it clearer?
Thread Synchronization and Dead-Locking.
Spending time on design, and spending time on refactoring.
Refactoring produces no client-visible work at all, which makes it the hardest thing in the project to justify working on.
As a second "not client-visible" problem, unit testing.
I was asked how the internet worked - I responded with "SYN, ACK, ACK". Keep forgetting it's SYN, SYN-ACK, ACK..
(source: inetdaemon.com)
My most difficult question began innocently enough: my girlfriend asked how text is rendered in Firefox. I answered simply with something along the lines of "rendering engine, Gecko, HTML parser, blah blah blah."
Then it went downhill. "Well how does Gecko know what to display then?"
It spiraled from there quite literally down to the graphics drivers, operating system, compilers, hardware archiectures, and the raw 1s and 0s. I not only realized there were significant gaps in my own knowledge of the layering hierarchy, but also how, in the end, I had left her (and me!) more confused than when I began.
I should've initially answered "turtles all the way down" and stuck with that. :P
I had a fun case of trying to explain why a program wasn't behaving as expected when some records in a database had empty strings and some were NULL. I think their head just about exploded when I told them empty string is just a string with 0 bytes in it while NULL means unknown value and so you can't actually compare it to anything.
Afterward I had one nasty headache.
1.) SQL: Thinking in sets, rather than procedurally (it's hard enough for us programmers to grasp!).
2.) ...and here's a great example of demystifing technical concepts:
How I explained REST to my wife
A lot of statements starting with "It's because in Oracle, ..." come to my mind.
The biggest hurdles are around "technological debt", especially about how the architecture was correct for this version but needs to be changed for next version. This is similar to the problem of explaining "prototype versus production" and "version 1.0 versus version 2.0".
Worst mistake I ever made was doing a UI mockup in NeXT steps UI Builder. It looked exactly like the end product would look and had some behaviour. Trying to explain that there was 6 months of work remaining after that was very difficult.
How recursion works...
Why code like this is bad:
private void button1_Click(object sender, EventArgs e)
{
System.Threading.ThreadStart start =
new System.Threading.ThreadStart(SomeFunction);
System.Threading.Thread thread = new System.Threading.Thread(start);
_SomeFunctionFinished = false;
thread.Start();
while (!_SomeFunctionFinished)
{
System.Threading.Thread.Sleep(1000);
}
// do something else that can only be done after SomeFunction() is finished
}
private bool _SomeFunctionFinished;
private void SomeFunction()
{
// do some elaborate $##%#
_SomeFunctionFinished = true;
}
Update: what this code should be:
private void button1_Click(object sender, EventArgs e)
{
SomeFunction();
// do something else that can only be done after SomeFunction() is finished
}
private void SomeFunction()
{
// do some elaborate $##%#
}
The importance of unit tests.
"Adding a new programmer a month to this late task will make it ship later. Never mind, read this book." (The Mythical Man-Month.) Managers still don't quite get it.
The concept of recursion - some people get it really hard.
I sometimes really have hard time explaining the concept of covariance/contravariance and the problems related to them to fellow programmers.
Convincing a friend that the Facebook application I developed really doesn't store her personal data (e.g. name) even though still displays it.
Why it'll take another four weeks to put this app into production. After all, it only took a week to do the rapid prototype. It "works" (or at least looks like it does) so I should be pretty much finished, shouldn't I?
Explanations that involve security, code quality (maintainability), normalized DB schemas, testing, etc. usually come off as a list of abstractions that don't have any visible effect on the app, so it's hard to explain what they really contribute to the project and why they're necessary. Sometimes analogies can only take you so far.
C pointers
*i
&i
Avoiding Dead-Locking in a multi-threaded environment.
I cleared confusion by explaining it visually on a white-board, drawing out two parallel lines and showing what happens when the reach the same points at the same time.
Also role-playing two threads with the person I was explaining it to, and using physical objects (book, coffee mug, etc) to show what happens when we both try to use something at once.
There's really no right or wrong answer-proper for this... it's all experiences.
The hardest thing I have had to explain to a non-tech person was why he couldn't get to his website when traveling abroad but his family member that lived there (with a totally different provider) could get to it. Somehow, "Fail in Finland" wasn't good enough.
The most difficult concepts to explain to people I would label programmers as opposed to developers are some of the most core paradigms of object orientated design. Most specifically abstraction, encapsulation and the king, polymorphism and how to use them correctly.
Expanding on that is the level of complexity of explaining what Inversion of Control is and why it is an absolute need and not just extra layers of code that doesn't do anything.
I was going to comment on Mikael's post, that some people just take the sequential programming and unfortunately just stay with that.
But that really means: two seriously hard to explain concepts:
monads in haskell (usually starting with: "That's like a function that returns a function that does what you really wanted to do, but ...")
deferreds in twisted/python ("That's like... ehhh... Just use it for a year or so and you'll get it" ;) )
Trying to explain why code was executed sequentially at all. Seemingly this is not at all intuitive for some non-programmers (i.e. my girlfriend).
Why you do not need character correct index handling in most cases when you use UTF-8 strings.
It's hard to explain why most software has bugs. Many non-technical people have no idea how complex software is, and how easy it is to overlook unexpected conditions. They think we are just too lazy to fix stuff that we know is broken.
There are 10 different types of people in the world.
The people who understand Binary and the people who dont....
To put it plainly, why development is the most difficult concept ever exposed to man kind. Not related to any programming language, but in general. And no I am not trying to provide myself or you with an ego boost, the only real limitations to this field is your mind.
Why? We don't work with constants and there are no boundaries, the only reason an AI that thinks like a human being doesn't exist yet is due to our own limitations. All other aspects need to adhere to some sort of law, development doesn't care about the laws of physics or any law for that matter hence the term development... evolution.