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# Exercises
**THIS IS CURRENTLY HIGHLY WORK IN PROGRESS**
Here there should be a set of exercise problems for those wishing to pursue [LRS](lrs.md) in any way.
{ Hmmm, it's hard to figure out exactly what to put here. ~drummyfish }
Here there should be some exercises for those wishing to pursue [LRS](lrs.md) in any way.
## Programming Challenges
See also [needed projects](needed.md).
Here you will find suggestions for programming projects primarily focused on practicing programming, but made so that they can theoretically be expanded to something useful as well. They will be roughly sorted by difficulty (under each level projects will be approximately sorted by difficulty too). You can use this to practice what you've learned in [C tutorial](c_tutorial.md). Try to follow the [LRS](lrs.md) principles. We more or less assume you'll be programming in [C](c.md) -- that's how we judge the difficulty etc. -- but of course no one is stopping you from using another language, just remember it may become much more easy or difficult.
This place is for suggesting programming projects that will in first place serve practicing [programming](programming.md), but they'll be formulated so that they can theoretically be expanded to something useful in the end. The projects will be roughly sorted from easiest to hardest into different difficulty levels and within each level also at least approximately from easiest to hardest. You can use this to practice what you've learned in [C tutorial](c_tutorial.md). Be sure to follow the [LRS](lrs.md) principles. We more or less assume you'll be programming in [C](c.md) -- that's how we judge the difficulty etc. -- but of course no one is stopping you from using another language, just remember it may become much more easy or difficult or just awkward.
**LRS programming challenge!** If you desire "motivation", treat this as a [game](game.md), the projects are achievements you can collect. Then it would be cool if you make a git repo or something to show it to the world { I'll be glad to see it, drop me a link :) ~drummyfish } Here are the rules:
**LRS programming challenge!** If you desire "motivation", feel free to treat this as a [game](game.md), the projects will be achievements for you to collect. Then it would be cool if you make a [git](git.md) repo or something to show it to the world { I'll be glad to see it, drop me a link :) ~drummyfish } Here are the **rules**:
- Award yourself points like this:
- 1 point for a completed project in level 0.
@ -24,6 +20,7 @@ Here you will find suggestions for programming projects primarily focused on pra
- A project is considered completed only if you REALLY complete all of its requirements! It's not enough to say "mmm, I could do this if I wanted" -- no, you have to REALLY DO IT for it to count. If the requirement is to make a complete game, a buggy demo doesn't count. Also if you just use some cheat, use 100 libraries to do everything for you, you know you didn't really complete it :) If it's obvious implementing something is part of the challenge (for example collision detection in physics engine), you cannot use a library for it, you have to do it yourself. Just be honest with yourself.
- You CANNOT award yourself partial points, i.e. if you meet 90% of requirements for some project, you CANNOT give yourself 90% points for it, not even one point. Complete it 100%, then get 100% points. Again, it doesn't count to say "mmm, I could finish this if I wanted" -- no, until you finish it it's not finished. This is part of the challenge and insisting on it also makes you potentially make a nice, tidy program that will increase good in the world ;)
- You may reuse your own code without it counting as third party library, i.e. if you write 3D renderer in one project, you can use it in writing 3D game as another project, with it counting as if you wrote everything from scratch just for that project.
- The *thumbs up* parts are not mandatory, just a little extra challenge.
- Don't [cheat](cheating.md), you're only cheating yourself :)
- If there is any doubt, [drummyfish](drummyfish.md) is the arbiter. So if you for example don't know if your project passes, send it to drummyfish and he will tell you.
@ -35,7 +32,8 @@ Here you will find suggestions for programming projects primarily focused on pra
4. **password generator**: Make a program which when run outputs randomly generated password (the password must be different each time you run the program of course). The password must be at least 10 characters long, contain at least one decimal digit and one special character.
5. **rock, paper scissors**: Make a game of rock paper scissors, the player plays against the computer.
6. **average**: Make a program that reads two numbers (you can assume only non-negative integers will be input) and writes out their average (it can be rounded, even to just integer, e.g. 3 and 8 can give 5).
7. **[Nim](nim.md)**: Implement the simple variant of the game Nim for two human players -- At the beginning there will be 15 matches, players take turn, in each turn a player can take 1, 2 or 3 matches. That who takes the last one loses. The game has to show the number of matches as a numeral and also as some kind of symbols, for example: `|||||||||||||||`. Players have to input `1`, `2` or `3` to play their turn, on wrong input the game has to report error and ask again. At the end winner must be shown. Thumbs up for randomly setting the initial number of matches between 10 and 15.
7. **kawaii filter**: Make a program that will filter input text to make it more kawai senpai. It has to read characters from input until end is reached (you can consider either EOF or end of line the end of input, that's up to you), outputting each character it reads as soon as it reads it, except for letters *r*/*R* that will be replaced with *w*/*W*. Also when period is read, the word *desu* must be output before it. For example the input *"This program is really good."* will produce output *"This pwogwam is weally good desu."*.
8. **[Nim](nim.md)**: Implement the simple variant of the game Nim for two human players -- At the beginning there will be 15 matches, players take turn, in each turn a player can take 1, 2 or 3 matches. That who takes the last one loses. The game has to show the number of matches as a numeral and also as some kind of symbols, for example: `|||||||||||||||`. Players have to input `1`, `2` or `3` to play their turn, on wrong input the game has to report error and ask again. At the end winner must be shown. Thumbs up for randomly setting the initial number of matches between 10 and 15.
### Level 1: Easy, *I'm Too Young To Die*
@ -58,13 +56,14 @@ Here you will find suggestions for programming projects primarily focused on pra
3. **[gopher](gopher.md) browser**: Write interactive gopher browser -- it can be a purely [command line](cli.md) browser. It has to be able to follow links and go back at least one page. The program must include some basic help and ability to save files to disk.
4. **simple text [compression](compression.md)**: Write a program that can compress and decompress plain [ASCII](ascii.md) text files using some very simple technique like [run length encoding](rle.md) (RLE) or dictionary methods (you can even use a fixed dictionary, e.g. have a list of common English words that you will represent by some shorter symbols). You can assume input characters will only have 7bit ASCII codes, so you can compress the text also by dropping the 8th unused bit. You don't have to achieve great compression ratio (you can even enlarge some files), but you must pass the following test: take the program's source code, this article's plain text and Wikipedia main page plain text, your program must compress at least two of these to a smaller size (and of course successfully decompress them into identical files). The program must work as a [filter](filter.md), i.e. it mustn't load the whole file into memory or perform multiple passes, it has to use approximately same amount of RAM for input of any size.
5. **stupid chatbot**: Make an entertaining chatbot that can react to basic sentences like "how are you?", "are you a robot?", "tell me a joke" and so on. It must give a human-like answer to at least 50 different sentences. It has to deal with typos and text variability a little bit (for example multiple spaces in a row or all caps text mustn't confuse it). It must have a mood meter which changes depending on what the partner says -- for example if the bot gets insulted, it gets more angry and starts inserting profanity to responses; on the other hand if it's happy it will insert nice smiley faces etc. The bot also has to remember and use the name of its chat partner if that is brought up. Test the bot by having it chat with itself.
6. **arbitrary size [rational numbers](rational_number.md)**: Make a library that allows working with arbitrary size rational numbers, i.e. represent each number as a pair of numerator and denominator, the number will be automatically allocating itself as much memory as it needs for storing the two internal values. Negative numbers must be supported too. It mustn't waste too much memory, i.e. whenever it changes, it will try to simplify the fraction and, if possible, decrease its size and allocate less memory. Size of the number will only be limited by amount of RAM your program can use. Furthermore implement these operations with the numbers: converting to/from the language's native numbers (with rounding if necessary), comparisons (equal, greater, greater or equal, smaller, smaller or equal), addition, subtraction, multiplication, division and printing and/or converting the number to string (at least decimal -- if the number has infinitely many fractional digits, just cut the output somewhere).
7. **image to [ASCII art](ascii_art.md)**: Make a program that takes an RGB bitmap image and renders it with ASCII characters (i.e. prints it out to console). You can support loading the image from just one file format of your choice, possibly something simple like PPM, BMP or Farbfeld. The program must support resizing the image and it must allow to just set one dimension with keeping the aspect ratio. Thumbs up for extra features like setting brightness/contrast and so on.
8. **educational [sorting](sorting.md) visualization**: Make a program for visualizing sorting algorithms -- it may draw real graphics (either directly to the screen or by outputting animation file) or just render ASCII art graphics, but it has to clearly show what the sorting algorithm is doing, i.e. which elements are being compared, which are swapped and if it makes good sense to highlight something else (like the pivot or already sorted part of the array), you should do it. Implement at least bubble sort, insertion sort, selection sort and quick sort. Also offer benchmark mode in which all algorithms race in sorting the same array (this can be without advanced visualization, just show e.g. number of steps for each).
9. **3D model of [fractal](fractal.md)**: Make a program that outputs 3D model of either Siepinski triangle or Koch snowflake fractal. The output shall be some simple 3D format like obj or Collada. The model can be primitive, i.e. it can be just flat shape made of triangles which don't have to really be connected, but the program must allow specifying the number of iterations of the fractal (during invocation, e.g. as a CLI flag). Check that the model is correct by opening it in some 3D editor such as Blender.
10. **[steganography](steganography.md)**: Make a program that hides text strings in either pictures, sounds or another text. The program must be a nice [CLI](cli.md) utility that performs both encoding and decoding -- it will allow the user to specify the string to hide (this string can be simplified to take less space, e.g. it may be converted to all caps, special characters may be removed etc.) and the data in which to embed them. The size of the string that can be encoded will of course be limited by how much space there is in the data, so you can reject or shorten the string if that's the case. The string must NOT be hidden in metadata (i.e. exif tags, file header, after the data, ...), it must be encoded in the useful data itself, i.e. in pixels of the picture, samples of the sound or characters of the text, but it mustn't be apparent that there is something hidden in the data. Use some simple technique, for example in images and sound you can often change the least significant bits without it being noticed, in text you can insert typos, hyphens, replace some periods with semicolons etc. Get creative.
11. **[sudoku](sudoku.md) solver**: Create a program to which the user somehow passes a sudoku puzzle (in a file, through a CLI flag, interactively... the choice is yours, but passing a new puzzle mustn't require program recompilation) and the program attempts to solve it. It must first employ some basic reasoning, at very least it has to repeatedly try the elimination method, i.e. marking a set of possible values in each empty square and then reducing these sets by crossing out values that can't be in that square because the same value is in its column/row/minisquare -- wherever only one value remains in the set, it is filled in as final; this has to be repeated until no more progress is being made. If you want, you can employ other techniques as well. After this if the puzzle is still not solved, the program will resort to [brute force](brute_force.md) which has to eventually lead to solution (even if it would take too long). If the program finds that the puzzle is unsolvable, it has to report it.
12. **language recognizer**: Make a program that will be able to learn and then recognize language of text it is given (in theory it should work for any kind of language, be it human or computer language). Specifically the program will first get *N* files, each one representing a different language (e.g. 5 books in different human languages), then it will take some other text and say to which of the initial *N* files it is linguistically most similar. For simplicity assume only plain ASCII files on input (you can just use some Unicode to ASCII utility on all input files). Use some simple [machine learning](machine_learning.md) technique such as some variant of k-NN. It will suffice if for each training example you construct a vector of some nice features, for example {average word length, vowel/consonant ratio, relative frequency of letter A, relative frequency of letter E, ...}, give each component some weight and then just find the nearest neighbour to the tested sample in this feature space (if you want to be more fancy, split the input files into parts so you get more training samples, then try k-NN with some convenient k). You shouldn't and CANNOT use neural networks, and of course you CANNOT use any machine learning library ;) You don't have to achieve great accuracy but your program should likely be able to quite reliably tell e.g. German from C++.
6. **[minesweeper](minesweeper.md)**: Implement the minesweeper game! It can be a purely command line program if you manage to render it well with ASCII art and make controls usable, but of course you can try making it GUI as well. There must be at least three difficulty levels that differ by board size and number of mines. First click must never land on a mine. The game must show the time it took to complete it, thumbs up for implementing a persistent top 3 score board that's saved to a file.
7. **arbitrary size [rational numbers](rational_number.md)**: Make a library that allows working with arbitrary size rational numbers, i.e. represent each number as a pair of numerator and denominator, the number will be automatically allocating itself as much memory as it needs for storing the two internal values. Negative numbers must be supported too. It mustn't waste too much memory, i.e. whenever it changes, it will try to simplify the fraction and, if possible, decrease its size and allocate less memory. Size of the number will only be limited by amount of RAM your program can use. Furthermore implement these operations with the numbers: converting to/from the language's native numbers (with rounding if necessary), comparisons (equal, greater, greater or equal, smaller, smaller or equal), addition, subtraction, multiplication, division and printing and/or converting the number to string (at least decimal -- if the number has infinitely many fractional digits, just cut the output somewhere).
8. **image to [ASCII art](ascii_art.md)**: Make a program that takes an RGB bitmap image and renders it with ASCII characters (i.e. prints it out to console). You can support loading the image from just one file format of your choice, possibly something simple like PPM, BMP or Farbfeld. The program must support resizing the image and it must allow to just set one dimension with keeping the aspect ratio. Thumbs up for extra features like setting brightness/contrast and so on.
9. **educational [sorting](sorting.md) visualization**: Make a program for visualizing sorting algorithms -- it may draw real graphics (either directly to the screen or by outputting animation file) or just render ASCII art graphics, but it has to clearly show what the sorting algorithm is doing, i.e. which elements are being compared, which are swapped and if it makes good sense to highlight something else (like the pivot or already sorted part of the array), you should do it. Implement at least bubble sort, insertion sort, selection sort and quick sort. Also offer benchmark mode in which all algorithms race in sorting the same array (this can be without advanced visualization, just show e.g. number of steps for each).
10. **3D model of [fractal](fractal.md)**: Make a program that outputs 3D model of either Siepinski triangle or Koch snowflake fractal. The output shall be some simple 3D format like obj or Collada. The model can be primitive, i.e. it can be just flat shape made of triangles which don't have to really be connected, but the program must allow specifying the number of iterations of the fractal (during invocation, e.g. as a CLI flag). Check that the model is correct by opening it in some 3D editor such as Blender.
11. **[steganography](steganography.md)**: Make a program that hides text strings in either pictures, sounds or another text. The program must be a nice [CLI](cli.md) utility that performs both encoding and decoding -- it will allow the user to specify the string to hide (this string can be simplified to take less space, e.g. it may be converted to all caps, special characters may be removed etc.) and the data in which to embed them. The size of the string that can be encoded will of course be limited by how much space there is in the data, so you can reject or shorten the string if that's the case. The string must NOT be hidden in metadata (i.e. exif tags, file header, after the data, ...), it must be encoded in the useful data itself, i.e. in pixels of the picture, samples of the sound or characters of the text, but it mustn't be apparent that there is something hidden in the data. Use some simple technique, for example in images and sound you can often change the least significant bits without it being noticed, in text you can insert typos, hyphens, replace some periods with semicolons etc. Get creative.
12. **[sudoku](sudoku.md) solver**: Create a program to which the user somehow passes a sudoku puzzle (in a file, through a CLI flag, interactively... the choice is yours, but passing a new puzzle mustn't require program recompilation) and the program attempts to solve it. It must first employ some basic reasoning, at very least it has to repeatedly try the elimination method, i.e. marking a set of possible values in each empty square and then reducing these sets by crossing out values that can't be in that square because the same value is in its column/row/minisquare -- wherever only one value remains in the set, it is filled in as final; this has to be repeated until no more progress is being made. If you want, you can employ other techniques as well. After this if the puzzle is still not solved, the program will resort to [brute force](brute_force.md) which has to eventually lead to solution (even if it would take too long). If the program finds that the puzzle is unsolvable, it has to report it.
13. **language recognizer**: Make a program that will be able to learn and then recognize language of text it is given (in theory it should work for any kind of language, be it human or computer language). Specifically the program will first get *N* files, each one representing a different language (e.g. 5 books in different human languages), then it will take some other text and say to which of the initial *N* files it is linguistically most similar. For simplicity assume only plain ASCII files on input (you can just use some Unicode to ASCII utility on all input files). Use some simple [machine learning](machine_learning.md) technique such as some variant of k-NN. It will suffice if for each training example you construct a vector of some nice features, for example {average word length, vowel/consonant ratio, relative frequency of letter A, relative frequency of letter E, ...}, give each component some weight and then just find the nearest neighbour to the tested sample in this feature space (if you want to be more fancy, split the input files into parts so you get more training samples, then try k-NN with some convenient k). You shouldn't and CANNOT use neural networks, and of course you CANNOT use any machine learning library ;) You don't have to achieve great accuracy but your program should likely be able to quite reliably tell e.g. German from C++.
### Level 3: Hard, *Ultra Violence*
@ -120,9 +119,10 @@ Here are some questions to test your LRS related knowledge :D
20. In 3D computer [graphics](graphics.md) what's the difference between [shading](shading.md) and drawing [shadows](shadow.md)?
21. Can we say that the traditional feed forward [neural networks](neural_network.md) are [Turing complete](turing_complete.md)? Explain why or why not.
22. Wicw mx uum yvfe bbt uhmtf ok?
23. What is the principle of [asymmetric cryptography](asymmetric_cryptography.md) and why is it called *asymmetric*?
24. WARNING: VERY HARD. There are two integers, both greater than 1 and smaller than 100. *P* knows their product, *S* knows their sum. They have this conversation: *P* says: I don't know the numbers. *S* says: I know you don't, I don't know them either. *P* says: now I know them. *S* says: now I know them too. What are the numbers? To solve this you are allowed to use a programming language, pen and paper etc. { Holy shit this took me like a whole day. ~drummyfish }
25. Did you enjoy this quiz?
23. Does the statement "10 does not equal 10" logically [imply](implication.md) that intelligent alien life exists?
24. What is the principle of [asymmetric cryptography](asymmetric_cryptography.md) and why is it called *asymmetric*?
25. WARNING: VERY HARD. There are two integers, both greater than 1 and smaller than 100. *P* knows their product, *S* knows their sum. They have this conversation: *P* says: I don't know the numbers. *S* says: I know you don't, I don't know them either. *P* says: now I know them. *S* says: now I know them too. What are the numbers? To solve this you are allowed to use a programming language, pen and paper etc. { Holy shit this took me like a whole day. ~drummyfish }
26. Did you enjoy this quiz?
### Answers
@ -148,10 +148,11 @@ Here are some questions to test your LRS related knowledge :D
20. Shading is the process of computing surface color of 3D objects, typically depending on the object's material and done by GPU programs called [shaders](shader.md); shading involves for example applying textures, normal mapping and mainly lighting -- though it can make pixels lighter and darker, e.g. depending on surface normal, it only applies local models of light, i.e. doesn't compute true shadows cast by other objects. On the other hand computing shadows uses some method that works with the scene as a whole to compute true shadowing of objects by other objects.
21. We can't really talk about Turing completeness of plain neural networks, they cannot be Turing complete because they just transform fixed length input into fixed length output -- a Turing complete model of computation must be able to operate with arbitrarily large input and output. In theory we can replace any neural network with logic circuit or even just plain lookup table. Significance of neural networks doesn't lie in their computational power but rather in their efficiency, i.e. a relatively small and simple neural network may replace what would otherwise be an enormously large and complicated circuit.
22. two (or txq); The cipher offsets each letter by its position.
23. The main difference against symmetric cryptography is we have two keys instead of one, one (private) for encrypting and one (public) for decrypting -- neither key can be used for the other task. Therefore encryption and decryption processes differ greatly (while in symmetric cryptography it's essentially the same, using the same key, just in reversed way), the problem looks different in one direction that the other, hence it is called *asymmetric*.
24. 4 and 13, solution: make a table, columns are first integer, rows are second (remember, both *P* and *S* can be making their own table like this too). Cross out whole bottom triangle (symmetric values). *P* doesn't know the numbers, so cross out all combinations of two primes (he would know such numbers as they have only a unique product). *S* knew *P* didn't know the numbers, so the sum also mustn't be a sum of two primes (if the sum could be written as a prime plus prime, *S* couldn't have known that *P* didn't know the numbers, the numbers may have been those two primes and *P* would have known them). This means you can cross out all such numbers -- these are all bottom-left-to-top-right diagonals that go through at least one already crossed out number (combination of primes), as these diagonal have constant sum. Now *P* has a table like this with relatively few numbers left -- if he now leaves in only the numbers that make the product he knows, he'll very likely be left with only one combination of numbers -- there are still many combinations like this, but only the situation when the numbers are set to be 4 and 13 allows *S* to also deduce the numbers after *P* declares he knows the numbers -- this is because *S* knows the combination lies on one specific constant-sum diagonal and 4-13 lie on the only diagonal that in this situation has a unique product within the reduced table. So with some other combinations *P* could deduce the numbers too, but only with 4-13 *S* can finally say he knows them too.
25. yes
23. Yes, a false statement implies anything.
24. The main difference against symmetric cryptography is we have two keys instead of one, one (private) for encrypting and one (public) for decrypting -- neither key can be used for the other task. Therefore encryption and decryption processes differ greatly (while in symmetric cryptography it's essentially the same, using the same key, just in reversed way), the problem looks different in one direction that the other, hence it is called *asymmetric*.
25. 4 and 13, solution: make a table, columns are first integer, rows are second (remember, both *P* and *S* can be making their own table like this too). Cross out whole bottom triangle (symmetric values). *P* doesn't know the numbers, so cross out all combinations of two primes (he would know such numbers as they have only a unique product). *S* knew *P* didn't know the numbers, so the sum also mustn't be a sum of two primes (if the sum could be written as a prime plus prime, *S* couldn't have known that *P* didn't know the numbers, the numbers may have been those two primes and *P* would have known them). This means you can cross out all such numbers -- these are all bottom-left-to-top-right diagonals that go through at least one already crossed out number (combination of primes), as these diagonal have constant sum. Now *P* has a table like this with relatively few numbers left -- if he now leaves in only the numbers that make the product he knows, he'll very likely be left with only one combination of numbers -- there are still many combinations like this, but only the situation when the numbers are set to be 4 and 13 allows *S* to also deduce the numbers after *P* declares he knows the numbers -- this is because *S* knows the combination lies on one specific constant-sum diagonal and 4-13 lie on the only diagonal that in this situation has a unique product within the reduced table. So with some other combinations *P* could deduce the numbers too, but only with 4-13 *S* can finally say he knows them too.
26. yes
## Other
Make your own exercises in daily life, adopt a mindset of taking small intellectual (or even non-intellectual) challenges. Don't slip into conformist consumerist life of comfort and ignorance that will make your brain rot. Learn new things just for the same of it -- make a game, learn a new language, learn to play music, learn chemistry, paint a picture, learn [chess](chess.md), read a whole [encyclopedia](encyclopedia.md), read Quran, solve puzzles in magazines, construct a machine out of wood, collect rocks, write a book, compose a song, ... you get the idea. Even if you just play vidya games, at least play some puzzle game or a strategy game, or a creative sandbox game, or invent some self-imposed challenge and make it into a puzzle game if it's not, or write a bot that plays the game for you, don't be just a zombie staring into screen. It's good to make it a habit to do some small exercise every day, such as play one game of chess with your computer every single day, or watch one video about math etc. -- in a year or two you'll become pretty good at a new skill just by this. WARNING: do not confuse this with the so called "[self improvement](productivity_cult.md)" cult, you'd be retarded to join that.
Make your own exercises in daily life, adopt a mindset of taking small intellectual (or even non-intellectual) challenges. Don't slip into conformist consumerist life of comfort and ignorance that will make your brain rot. Learn new things just for the sake of it -- make a game, learn a new language, learn to play music, learn chemistry, paint a picture, learn [chess](chess.md), read a whole [encyclopedia](encyclopedia.md), read Quran, solve puzzles in magazines, construct a machine out of wood, collect rocks, write a book, compose a song, multiply numbers in your head before sleep ... you get the idea. Even if you just play vidya games, at least play some puzzle game or a strategy game, or a creative sandbox game, or invent some self-imposed challenge and make it into a puzzle game if it's not, or write a bot that plays the game for you, don't be just a zombie staring into screen. It's good to make it a habit to do some small exercise every day, such as play one game of chess with your computer every single day, or watch one video about math etc. -- in a year or two you'll become pretty good at a new skill just by this. WARNING: do not confuse this with the so called "[self improvement](productivity_cult.md)" cult, you'd be retarded to join that.