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In my University tests I often have to write programs and algorithms with pen and paper. For example, for my next test I'm going to have to write quite a lot of code in scheme and Java on paper.
I write quite a lot of code, but never on pen and paper. When writing code on paper, I often go at it with the same attitude as if I'd be writing the code on a computer. This often results in a lot of strikethroughs and additions, which often results in a total incomprehensible mess, because I'm used to being able to add and remove blocks as I please.
The problem is the programs or algorithms are complex enough so that it's not possible to think them completely through in your head before writing the code.
Is there any way to effectively and efficiently write code with pen and paper?
You are right in writing the code on paper as you write it on the system. But, to write an efficient code, you need to learn few things
Always use indentation at every line of code to make it presentable
Don't forget to add comments at various points so that what you are writing and trying to convey gets clear to the examiner
If anywhere you want to cut through some parts of your code, or encounter a strikethrough, better strike out the whole line and rewrite it. It improves the visibility of the code and makes it appealing.
Remember to leave ample amount of space between two lines of codes, probably a blank line or two. This spacing makes your code presentable.
More suggestions are welcome.
Ugh... Programming on paper!! =(
When I am backed into a corner and forced to do this, I like to have a pad of scrap paper handy. I nut out the shape of the program on my scrap paper.. That means I draw a bunch of rectangles, roughly representing how much code I might have to write in a block. When I realise I need something else in between, I sketch more rectangles and draw obvious arrows.
A rectangle might say a few hasty words about what it's achieving, like load stuff from thing. Or x < y ? Or whatever helps me get a feel for what I think I'm going to write, without wasting too much time. I might also note down variable names I intend to use further down, and draw an arrows to where that may be... Or even write a line of code that I mustn't forget!
That means I already have an overview of what I'm doing before I start the code. It gives me time to sit back and make sure I have thought it through. Then I can focus on implementing small chunks at a time and keep my thinking more linear. That's useful because I make more mistakes if I'm thinking ahead at the same time as writing.
Works for me... Might be useful to you, or it might just sound like rubbish.
Related
i put a small request on upwork where i am requesting help for a topic which is right now out of my skill zone.
The problem is a fitting problem of small rectangles in a big rectangle via a ANN.
Problem is the first freelancer baffled me a little bit with a comment.
So my thinking was, because the solution is easy verified and rewardable, that you can simply throw a ANN on this problem and with enough time it will perform better and better.
The freelancer requested labeled data first before he can tackle the problem(thats the comment which confuses me).
I was thinking that unlabeled random Input data is enough for the start.
Do I think wrong?
here the link to the job post.
https://www.upwork.com/jobs/~01e040711c31ac0979
edit: directly the original job description
I want python code for training a ANN and using it in a productive enviroment.
The problem it needs to solve is a rectangle fitting problem.
Input are
1000 small Rectangles(groupid,width,heigth,Oriantion(free,restricted,hor or ver), value) --sRect
1 big Rectangles(width, heigth)--bRect
Layout(bool,bool,bool,xpos,ypos,Oriantaion(hor or ver))--Layout
Output
Layout
The bRect will be duplicated to 3 Rectangles where the sRects need to be fitted into.
The Worth of the solution is determined by the sum of the value of sRect inside the bRect.
Further is the value decreased if the sRect is placed in the second bRect or third bRect.
sum(sRect(value))*0.98^nth bRect
Not all sRect needs to be placed.
Layout is structered that the three bool at the start represent at which bRect the sRect is placed. If a sRect is placed at one of the bRect, then the Solution Layout muss stay for this sRect the same.
Restricted Ori means all of the sRect with the same group need to be Oriantated the same way. Hor means the sRect is not turned, ver the sRect is turned by 90degrees.
Other then that normal rules apply, like all sRect needs to be inside the bRect and not Overlapp between sRect.
Looking forward to replys and i am avaible for further explanations.
edit: example picture
important i dont want to optimise for maximum plate usage, because it can happen that a smaller sRect can have a higher value then a bigger sRect.
example fitting problem
Without expected output for each input you cannot use the most standard training methodology - supervised learning. If you only have a way to verify the solution (e.g. in a game of chess you can tell me if I won but you cant tell me how to win) then the most standard approach is reinforcement learning. That being said, it is much more complex problem, not something that say a newcomer to the field of ML will be capable of doing (while supervised learning is something that one can do essentially by following basic tutorials online)
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I am not a web programmer, but we all find ourselves needing to mess around with html, css, and javascript at some point. And every time I do, I find myself hating CSS's guts. This is almost entirely related to positioning. Many things that I think should be easy and straightforward turn out to be very difficult or even (seemingly) impossible.
Take centering something in the user's browser/interface. I recently wanted to do a "Coming Soon…" temporary splash page (cliche, I know), and I wanted a tiny piece of text or image to land right in the middle of the user's browser. Conceptually this couldn't be simpler, and yet to actually achieve this in CSS you have to do all kinds of tricks. I'm not asking how you achieve this. There are several tutorials/examples, including these two excellent ones:
http://css-tricks.com/centering-in-the-unknown/
http://www.dynamicsitesolutions.com/css/center-page-content-horizontally-and-vertically/
What I want to understand is why it is so complex to achieve something so basic? Why can't I just make a div (or whatever) that spans the height and width of the browser, and align something in the middle of that? Why do you have to come up with entire frameworks like Bootstrap (which, in my opinion, are still incomplete and hacky) to do things that should be a part of the philosophy of the implementation?
The people that come up with the CSS standard are much smarter than I am, and there must be a reason for this. What is their logic or philosophy behind how it is implemented? What am I missing? I want to understand, so at least next time I try to implement something I won't fool myself into thinking "This will be easy" when, I assume, there is a reason it can't be.
Because HTML/CSS is limited by its roots: ltr horizontal flow
When we first started making websites, HTML was designed as a simple way to make content flow, like in a magazine or a book. Maybe it would have images or embedded audio, but there was no way to foresee at the time that we would have websites in the millions of lines of code. HTML was designed with horizontal flow, not vertical flow in mind.
There are other examples of this:
It is comparatively difficult to vertically align text to the center or bottom of a page, this requires a lot of unintuitive understanding whereas central alignment on the horizontal plane is a simple text-align='center';
Tables are defined with <tr> table row tags, not <tc> table column tags.
Ever tried making a <DIV>, especially one wrapped inside other divs, the full height of the page (not screen)? It's not as easy as you'd think.
An element with height:100% is not automatically the same height as your browser, only the height of your content. See this example.
Because of the need to maintain backwards compatibility, browsers continue to use rendering engines based on left-to-right, top to bottom rendering. It seems unlikely that an alternative to HTML will take the web by storm any time soon, so we're probably stuck with this paradigm for the foreseeable future.
I am working on a simple drawing application, and i need an algorithm to make flood fills.
The user workflow will look like this (similar to Flash CS, just more simpler):
the user draws straight lines on the workspace. These are treated as vectors, and can be selected and moved after they are drawn.
user selects the fill tool, and clicks on the drawing area. If the area is surrounded by lines in every direction a fill is applied to the area.
if the lines are moved after the fill is applied, the area of fill is changed accordingly.
Anyone has a nice idea, how to implement such algorithm? The main task is basically to determine the line segments surrounding a point. (and storing this information somehow, incase the lines are moved)
EDIT: an explanation image: (there can be other lines of course in the canvas, that do not matter for the fill algorithm)
EDIT2: a more difficult situation:
EDIT3: I have found a way to fill polygons with holes http://alienryderflex.com/polygon_fill/ , now the main question is, how do i find my polygons?
You're looking for a point location algorithm. It's not overly complex, but it's not simple enough to explain here. There's a good chapter on it in this book: http://www.cs.uu.nl/geobook/
When I get home I'll get my copy of the book and see if I can try anyway. There's just a lot of details you need to know about. It all boils down to building a DCEL of the input and maintain a datastructure as lines are added or removed. Any query with a mouse coord will simply return an inner halfedge of the component, and those in particular contain pointers to all of the inner components, which is exactly what you're asking for.
One thing though, is that you need to know the intersections in the input (because you cannot build the trapezoidal map if you have intersecting lines) , and if you can get away with it (i.e. input is few enough segments) I strongly suggest that you just use the naive O(n²) algorithm (simple, codeable and testable in less than 1 hour). The O(n log n) algorithm takes a few days to code and use a clever and very non-trivial data structure for the status. It is however also mentioned in the book, so if you feel up to the task you have 2 reasons to buy it. It is a really good book on geometric problems in general, so for that reason alone any programmer with interest in algorithms and datastructures should have a copy.
Try this:
http://keith-hair.net/blog/2008/08/04/find-intersection-point-of-two-lines-in-as3/
The function returns the intersection (if any) between two lines in ActionScript. You'll need to loop through all your lines against each other to get all of them.
Of course the order of the points will be significant if you're planning on filling them - that could be harder!
With ActionScript you can use beginFill and endFill, e.g.
pen_mc.beginFill(0x000000,100);
pen_mc.lineTo(400,100);
pen_mc.lineTo(400,200);
pen_mc.lineTo(300,200);
pen_mc.lineTo(300,100);
pen_mc.endFill();
http://www.actionscript.org/resources/articles/212/1/Dynamic-Drawing-Using-ActionScript/Page1.html
Flash CS4 also introduces support for paths:
http://www.flashandmath.com/basic/drawpathCS4/index.html
If you want to get crazy and code your own flood fill then Wikipedia has a decent primer, but I think that would be reinventing the atom for these purposes.
Hey everyone,
I'm trying to create a program in Java that can read numbers of the screen, and also recognise images on the screen. I was wondering how i can achieve this?
The font of the numbers will always be the same. I have never programmed anything like this before, but my idea of how it works is to have the program take a screenshot, then overlay the image of the numbers with the section of the screenshot image and check if they match, repeating this for each numbers. If this is the correct way to do this, how would i put that in code.
Thanks in advance for any help.
You could always train a neural net to do it for you. They can get pretty accurate sometimes. If you use something like Matlab it actually has capabilities for that already. Apparently there's a neural network library for java (http://neuroph.sourceforge.net/) although I've never used it personally.
Here's a tutorial about using neuroph: http://www.certpal.com/blogs/2010/04/java-neural-networks-and-neuroph-a-tutorial/
You can use a neural network, support vector machine, or other machine learning construct for this. But it will not do the entire job. If you do a screen shot, you are going to be left with a very large image that you will need to find the individual characters on. You also need to deal with the fact that the camera might not be pointed straight at the text that you want to read. You will likely need to use a series of algorithms to lock onto the right parts of the image and then downsample it in a way that size becomes neutral.
Here is a simple Java applet I wrote that does some of this.
http://www.heatonresearch.com/articles/42/page1.html
It lets you draw on a relatively large area and locks in on your char. Then it recognizes it. I am using the alphabet, but digits should be easier. The complete Java source code is included.
One simpler approach could be to use template matching. If the fonts are same, and/or the size (in pixels)is known, then simple template matching can do the job for you. ifsize of input is unknown, you might have to create copies of images at different scales and do the matching at each scale.
One with the extreme value(highest or lowest depending on the method you follow for template matching) is your result.
Follow this link for details
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I'm teaching a kid programming, and am introducing some basic artificial intelligence concepts at the moment. To begin with we're going to implement a tic-tac-toe game that searches the entire game tree and as such plays perfectly. Once we finish that I want to apply the same concepts to a game that has too many positions to evaluate every single one, so that we need to implement a heuristic to evaluate intermediate positions.
The best thing I could think of was Dots and Boxes. It has the advantage that I can set the board size arbitrarily large to stop him from searching the entire tree, and I can make a very basic scoring function be the number of my boxes minus the number of opponent boxes. Unfortunately this means that for most of the beginning of the game every position will be evaluated equivalently with a score of 0, because it takes quite a few moves before players actually start making boxes.
Does anyone have any better ideas for games? (Or a better scoring function for dots and boxes)?
Another game choice could be Reversi aka Othello.
A naive heuristic would be to simply count the number of tiles gained by each valid move and choose the greatest. From there you can factor in board position and minimizing vulnerably to the opponent.
One game you may consider is Connect Four. Simple game with straightforward rules but more complicated that Tic-Tac-Toe.
Checkers will let you teach several methods. Simple lookahead, depth search of best-case-worst-case decisions, differences between short-term and long-term gains, and something they could continue to work on after learning what you want to teach them.
Personally I think that last bit is the most critical -- there are natural points in the AI development which are good to stop at, see if you can beat it, and then delve into deeper AI mechanisms. It keeps your student interested without being horribly frustrated, and gives them more to do on their own if they want to continue the project.
How about Reversi? It has a pretty nice space of heuristics based on number of pieces, number of edge pieces, and number of corner pieces.
How about Mancala? Only 6 possible moves each turn, and it's easy to calculate the resulting score for each, but it's important to consider the opponent's response, and the game tree gets big pretty fast.
Gomoku is a nice, simple game, and fun one to write AI for.
Rubik's Infinity's quite fun, it's a little bit like Connect Four but subtly different. Evauluating a position is pretty easy.
I knocked together a Perl script to play it a while back, and actually had to reduce the number of moves ahead it looked, or it beat me every time, usually with quite surprising tactics.
Four in a line Hard enough, but easy enough to come up with an easy working evaluation function, for example, (distance to four from my longest line - distance to four from my opponent's longest line)
I really like Connect Four. Very easy to program using a Minimax algorithm. A good evaluation function could be:
eval_score = 0
for all possible rows/lines/diagonals of length 4 on the board:
if (#player_pieces = 0) // possible to connect four here?
if (#computer_pieces = 4)
eval_score = 10000
break for loop
else
eval_score = eval_score + #computer_pieces
(less pieces to go -> higher score)
end if
else if (#player_pieces = 4)
eval_score = -10000
break for loop
end if
end for
To improve the program you can add:
If computer moves first, play in the middle column (this has been proven to be optimal)
Alpha-Beta Pruning
Move Ordering
Zobrist Hashes
How about starting your Dots and Boxes game with random lines already added. This can get you into the action quickly. Just need to make sure you don't start the game with any boxes.
Take a look at Go.
Simple enough for kid on very small boards.
Complexity scales infinitely.
Has a lot of available papers, algorithms and programs to use either as a scale or basis.
Update: reversi was mentioned, which is a simplified variant of Go. Might be a better choice.
In regards to a better heuristic for dots and boxes, I suggest looking at online strategy guides for the game. The first result on Google for "dots and boxes strategy" is quite helpful.
Knowing how to use the chain rule separates an OK player from a good one. Knowing when the chain rule will work against you is what separates the best players from the good ones.