@ -18,6 +18,8 @@ Firstly this means anything is allowed, any unethical, unfair business practice,
Secondly the idea of getting rid of a state in capitalism doesn't even make sense because **if we get rid of the state, the strongest corporation will become the state**, only with the difference that state is at least *supposed* to work for the people while a corporation is only by its very definition supposed to care solely about its own endless profit on the detriment of people. Therefore if we scratch the state, McDonalds or Coca Cola or Micro$oft -- whoever is the strongest -- hires a literal army and physically destroys all its competition, then starts ruling the world and making its own laws -- laws that only serve the further growth of that corporation such as that everyone is forced to work 16 hour shifts every day until he falls dead. Don't like it? They kill your whole family, no problem. 100% of civilization will experience the worst kind of suffering, maybe except for the CEO of McDonald's, the world corporation, until the planet's environment is destroyed and everyone hopefully dies, as death is what we'll wish for.
A typical "anarcho"capitalist is a redneck who probably thinks the only thing preventing him from beating a corporation at its own game is state holding him back with high taxes -- he thinks that if he's allowed to keep all his crops he'll become a beast starting his own business that will go on beating Facebook, i.e. he thinks that if he can keep all five of all five carrots he grows on his field, he will somehow become so powerful he can bring down an army of ten thousand men with the most advanced technology who by the way can now also keep all money it makes, because he heard this in some fairy tale about Henry Ford or something. Of course that's highly laughable and pathetic, but indeed typically [American](usa.md).
All in all, "anarcho" capitalism is advocated mostly by children who don't know a tiny bit about anything, by children who are being brainwashed daily in schools by capitalist propaganda, with no education besides an endless stream of ads from their smartphones, or capability of thinking on their own. However, these children are who will run the world soon. It is sad, it's not really their fault, but through them the system will probably come into existence. Sadly "anarcho" capitalism is already a real danger and a very likely future. It will likely be the beginning of our civilization's greatest agony. We don't know what to do against it other than provide education.
@ -6,7 +6,7 @@ Here there should be a set of exercise problems for those wishing to pursue [LRS
{ Hmmm, it's hard to figure out exactly what to put here. ~drummyfish }
## Programming Projects
## Programming Challenges
See also [needed projects](needed.md).
@ -19,7 +19,8 @@ Here you will find suggestions for programming projects, roughly sorted by their
- 4 points for a completed project in level 1.
- 16 points for a completed project in level 2.
- 64 points for a completed project in level 3.
- If you complete all projects in level *N*, you can automatically consider all projects of all lower levels completed as well, i.e. if you complete whole level 2, count yourself whole level 1 and 0 as well.
- 256 points for a completed project in level 4.
- If you complete all projects in level *N*, you can automatically consider all projects of all lower levels completed as well, i.e. if you complete whole level 2, count yourself whole level 1 and 0 as well. (Once achieved you'll keep it forever, i.e. if more projects later appear in given level that you won't have solved, it won't take away your lower level points.)
- A project is considered completed only if you really complete all the requirements! It is not enough to say "mmm, I could do this if I wanted" -- no, you have to REALLY DO 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.
@ -31,8 +32,9 @@ Here you will find suggestions for programming projects, roughly sorted by their
2. **counting**: Make a program that outputs numbers from 1 up to 100.
3. **guess a number**: Make a game in which the computer secretly thinks a number from 0 to 9 and the player guesses the number. The computer then says if the player won and what the secret number what.
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. **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).
6. **[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.
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.
### Level 1: Easy, *I'm Too Young To Die*
@ -43,9 +45,10 @@ Here you will find suggestions for programming projects, roughly sorted by their
5. **text adventure**: Make an interactive [CLI](cli.md) text adventure that will take an average player at least 10 minutes to finish. Part of game mechanics must involve inventory, i.e. picking up items, carrying them around and using them.
6. **calculator**: Make an interactive calculator -- it can be a purely [command line](cli.md) program into which user types expressions and your program evaluates them. The functionality must be at least on the level of the most plain physical calculators, i.e. it doesn't have to parse whole complex expressions, but it should be able to add, subtract, multiply, divide and find square roots. Results can be approximate, showing just 3 fractional decimal digits. Thumbs up for more features like handling expressions with brackets, having a variable storing last result, converting between bases and so on.
7. **[bytebeat](bytebeat.md)**: Make at least three cool sounding bytebeat songs.
8. **Lorem ipsum generator**: Create a program that generates gibberish text that looks like normal human text. Each time it is run, it will generate generally a different text that consists of 10 paragraphs; each paragraph ends with newline and consists of 5 to 10 sentences; each sentence consists of 3 to 10 words, starts with capital letter (other letters are lowercase) and ends with period. After period there is space except when it's the last period in a paragraph. Words are selected randomly from some set of words you define.
8. **Lorem ipsum [markdown](md.md) generator**: Create a program that generates gibberish text in markdown format that looks like normal human text. Each time it is run, it will generate generally a different text that consists of 3 to 5 sections, each section starts with a heading which starts with `# ` after which 3 to 5 words follow, then there are two newlines and then 3 to 5 paragraphs follow; each paragraph ends with two newlines, except for the last one in the document which only ends with one newline. Paragraph consists of 5 to 10 sentences; each sentence consists of 3 to 10 words, starts with capital letter (other letters are lowercase) and ends with period. About 1 in 20 words in paragraphs are highlighted -- highlight is either italic (the word is between `*`s) or bold (the word is between `**`s). After period there is space except when it's the last period in a paragraph (then there is no space). Words are selected randomly from some set of words that you define (have at least 10 different words). Thumbs up for also generating lists etc.
9. **Caesar cipher**: Make a program that encrypts/decrypts text with the simple cipher known as Caesar cipher, i.e. by offsetting each letter by certain fixed number *N* (e.g. with *N = 2* the letter *A* will become *C*, *B* will become *D* etc.). Assume just ASCII characters on input (encrypted output can be non-ASCII). You can just choose and hardcode some specific *N* but thumbs up for allowing to set any *N*. You can input/output text from/to standard input/output or files -- it's up to you -- also you can either make one program that does both encoding and decoding (e.g. depending on CLI flag) or make two programs, one for each task.
10. **[brainfuck](brainfuck.md) interpreter**: Make a program that interprets brainfuck. You may choose to read the input program either from standard input or from a file (the file may have some hardcoded name, e.g. your program will just look for a file named `program.bf` in the same directory). If the brainfuck program is invalid or runtime error occurs in it, you may just write out `error` and halt your interpreter. Thumbs up for making the interpreter nicer, e.g. allowing to pass input file name as a CLI argument, reporting more details about errors (e.g. its position in source code) and so on.
10. **filetype guesser**: Create a program that reads a file and guesses its file type. You can NOT use the file name, only the file content. First look at the [magic number](magic_number.md) (file signature) -- check at least PDF, JPEG, PNG, MP3, GIF and TAR. If this doesn't succeed, then see if 90% of bytes are printable ASCII characters: if so, then guess the file to be TXT, otherwise you may report unknown type (or optionally you can try some extra checks if you want).
11. **[brainfuck](brainfuck.md) interpreter**: Make a program that interprets brainfuck. You may choose to read the input program either from standard input or from a file (the file may have some hardcoded name, e.g. your program will just look for a file named `program.bf` in the same directory). If the brainfuck program is invalid or runtime error occurs in it, you may just write out `error` and halt your interpreter. Thumbs up for making the interpreter nicer, e.g. allowing to pass input file name as a CLI argument, reporting more details about errors (e.g. its position in source code) and so on.
### Level 2: Mid, *Hurt Me Plenty*
@ -53,7 +56,7 @@ Here you will find suggestions for programming projects, roughly sorted by their
2. **2D game**: Make a complete 2D game in which you control a character, with at least 5 levels. Genre is up to you, recommended is e.g. platformer or top-down shooter. The game must have "real" graphics, i.e. not just terminal ASCII art -- using a library like [SAF](saf.md), Allegro or [SDL](sdl.md) may be a good choice. Sounds are not required but thumbs up if you have them.
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?" and so on. It must give a human-like answer to at least 20 different sentences. It has to deal with typos and text variability a little bit (for example multiple spaces in a row mustn't confuse it) and has to have some kind of memory (for example it can remember the name of its chatting partner or it can have something like mood meter). Test the bot by having it chat with itself.
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 numbers. It mustn't waste too much memory, i.e. whenever it changes, it will try to reallocate its memory and decrease its size if possible. 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).
@ -63,8 +66,8 @@ Here you will find suggestions for programming projects, roughly sorted by their
### Level 3: Hard, *Ultra Violence*
1. **non-trivial [programming language](programming_language.md)**: Design language *L* and make an interpreter for it. *L* must be [Turing complete](turing_complete.md) and you have to provide mathematical proof of it. *L* must allow [recursive](recursion.md) function calls. It must not support native [OOP](oop.md). *L* must be usable for programming very basic things -- show it is so by writing [bubble sort](bubble_sort.md) in it. Write [quine](quine.md) in it. Thumbs up for also making a compiler.
2. **radiation hardened quine**: Without looking it up, write radiation hardened [quine](quine.md) in some language. Quine is a program that outputs its own source code (don't cheat, you can't read it from the source file), radiation hardened quine is a quine that remains a quine if you remove any single character from the program.
1. **[quine](quine.md) master**: Without looking it up, write a quine in one language and radiation hardened quine in another language. Quine is a program that outputs its own source code (don't cheat, you can't read it from the source file), radiation hardened quine is a quine that remains a quine if you remove any single character from the program.
2. **non-trivial [programming language](programming_language.md)**: Design language *L*, write its specification and make a self hosted interpreter and/or compiler for it, i.e. write *L* in *L* (for this you may first have to write it in another language). *L* must be [Turing complete](turing_complete.md) and you have to provide mathematical proof of it. *L* must allow [recursive](recursion.md) function calls. It must not support native [OOP](oop.md). *L* must be usable for programming very basic things -- show it is so by writing [bubble sort](bubble_sort.md) in it. Write [quine](quine.md) in it. Thumbs up for also making a compiler.
3. **3D game**: Make a complete game with 3D graphics from 1st or 3rd man perspective that will have at least half an hour worth of gameplay time -- the gameplay can really be 2D (e.g. like [wolf3D](wolf3d.md)) but the graphics must be judged as 3D by average guy who sees the game. If your platform allows it at all, it must have basic sounds (no need for music, but e.g. shooting should at least make beeps and so on). The genre is up to you, it can be a shooter, platformer, RPG or anything where you control a character. For the 3D graphics you can either use a 3D library, in which case you HAVE TO implement textured graphics (the textures may be [procedural](procgen.md) if you want), or you can write your own renderer. If you write custom renderer, then if it's a "true 3D", it can have just flat, untextured graphics; if it's a "[pseudo 3D](pseudo3d.md)" (like raycasting or BSP, ...), it must have at least some texturing (e.g. walls).
4. **textured 3D [software renderer](sw_rendering.md)**: Make 3D software renderer that rasterizes triangles (just like for example [OpenGL](ogl.md)), with texturing. Affine texture mapping (i.e. the easier, incorrect texturing by linear interpolation of texturing coordinates in screen space) will pass, but thumbs up for perspective correct texture mapping. Implement some basic [shading](shading.md) like, e.g. Goraud with ambient and diffuse light. You have to handle visibility even of non-convex shapes, e.g. with z-buffer or at least approximately by sorting triangles. It's enough if you can display some textured model with setting camera position and rotation somehow. You don't have to handle any 3D formats, 3D models can just be passed as arrays of numbers (same with textures). It is enough if you output static images e.g. to a file, but thumbs up for being able to handle real-time rendering, animation and having extra features like transparency, scene graph and so on. Extra thumbs up for not using [float](float.md).
5. **[regular expression](regex.md) library**: Make a library for working with regular expressions. Implement at least the following operations: search of regular expression, substitution of regular expressions WITH capture groups and generating random strings by regular expression.
@ -74,6 +77,8 @@ Here you will find suggestions for programming projects, roughly sorted by their
9. **3D [path tracer](path_tracing.md) without [floating point](float.md)**: Write a path tracer (NOT a mere [ray tracer](ray_tracing.md)) without using floating point. It can only produce static images that may just be saved to a file in some simple format (no need to draw real time animation to the screen). It must be possible to position and rotate the camera arbitrarily and to set its field of view. It has to support several shapes of objects in the scene: at least a sphere, plane and cylinder, and it must support transparent objects. Thumbs up for supporting polygonal models, depth of field and loading scene description from a file.
10. **[gopher](gopher.md) fulltext search engine**: Create a whole search engine (with crawler, index creator, user frontend, ...) for the gopher network. It can store its database just to flat files (no need to use SQL or something like that). It has to allow at least very basic fulltext search, i.e. about each gopher site you'll have to remember which words it contains (and possibly their count), so that if the user searched e.g. for `cats dogs`, you'll give him sites that contain both of these words somewhere in their text -- offer options to search either for sites containing all searched words or just some of them. Besides this you can make simplifications (ignore case, don't support Unicode, special characters etc.). Thumbs up for additional features like creating a graphical map of the crawled gopherspace along the way.
11. **[Jpeg](jpg.md) clone**: Create a usable format for photo images with lossy [compression](compression.md), similar to [Jpeg](jpg.md), that achieves good compression ratio and allows setting compression level, including setting compression level 0 (when it will only apply lossless compression). The format doesn't have to store any metadata, it's enough if it holds a 24 bit RGB bitmap of arbitrary resolution. For compression it must do at least following: separating the color and intensity channel and subsampling the color channel (see e.g. [YCbCr](ycbcr.md)), then converting the image to frequency domain (probably with [discrete cosine transformation](dct.md)) and quantizing the high frequencies, and then applying at least some lossless compression (RLE or Huffman coding or something). You can't use any libraries to do the described things (e.g. DCT, color conversion etc.), do it all yourself. The program, with medium compression level set, has to beat lz4 at compressing photos at least 90% times (in theory it should win always but we'll give you some margin if you fuck something up).
12. **console [emulator](emulation.md)**: Make an emulator of either [PlayStation 1](ps1.md), Nintendo64, GameGear or any version of [GameBoy](gameboy.md) (GB, GBC or GBA). You can use a library for 3D rendering if you need it. You don't have to implement networking or weird/non-standard features (like light sensor etc.). You don't have to achieve high accuracy but at least a few games should be playable. You have to allow saving/loading game states. Sound support can be basic.
13. **[genetic programming](genetic_programming.md)**: Create a [KISS](kiss.md) genetic programming framework. Make some kind of simple, low level model of computation, its language (something like Turing machine, brainfuck, Forth etc.) and its interpreter, then implement firstly generating random programs, secondly randomizing (mutating) existing programs and thirdly combining existing programs (creating offspring). Now create a system that will spawn a population of random programs and will then direct its evolution by generations toward optimizing performance at some given task -- this performance will be measured by fitness function (which will somehow score any given program depending on how well it's working) that will be customizable in your framework, i.e. anyone must be easily able to rewrite the fitness function to whatever he desires (it's okay if changing fitness function requires recompilation of your program). In each generation your framework will remove badly performing programs, breed new programs by combining well performing ones, randomly mutate some programs and add in a few new completely random programs -- specific parameters of this must also be curstomizable (again, recompilation here is okay). Test this by evolving some simple program (solving a maze, quadratic equation, blurring an image or something similar).
### Level 4: God Tier, *!Nightmare!*
@ -81,11 +86,12 @@ Here you will find suggestions for programming projects, roughly sorted by their
2. **[operating system](operating_system.md)**: Make a whole [self hosted](self_hosting.md) operating system with your own custom kernel, with basic [GUI](gui.md) and tools such as a text editor, file browser and programming language compiler. Throw in some games because without them your OS will be boring. Run the OS on real hardware. It doesn't have to support networking, sound, USB and similar bloat, but thumbs up if you manage even that.
3. **[MMORPG](mmorpg.md)**: Make both client and server for an MMORPG game. The game has to support 3D graphics (but can also have 2D frontends) and have some basic lore that makes sense. Remember, it is MASSIVELY multiplayer game, so you have to be able to handle at least 1000 players connected at the same time on some kind of affordable computer. There must be chat, PvP and PvE combat. Thumbs up for releasing it all under [CC0](cc0.md).
4. **[Python](python.md)**: Implement the Python programming language, INCLUDING its whole standard library. Bonus points for finishing before the version you are implementing stops being supported.
5. **ruin [bitcoin](bitcoin.md)**: Make a program that can mine one bitcoin by running for at most one minute on some consumer laptop released before year 2010. Warning: this is probably unsolvable, but if you solve it you may help save the planet :P
5. **the grandest program of all time**: Make a program that (in a simplified way but still) simulates the whole [Universe](universe.md) and allows its user to explore and zoom in on anything not just in vast space but mainly on Earth, in big and small scales AND in all times in past and future, while the simulation approximately matches our available data (i.e. recorded historical events, famous people, geography, known bodies in the Universe etc.) and procedurally generates/interpolates/extrapolates unknown data (i.e. for example if we don't know what Napoleon did on a certain day, the program will make some guess and show him doing something). This will be the great visual encyclopedia in which one can observe the big bang, [Jesus](jesus.md), dinosaurs, black holes, the future destruction of Earth and so on.
6. **ruin [bitcoin](bitcoin.md)**: Make a program that can mine one bitcoin by running for at most one minute on some consumer laptop released before year 2010. Warning: this is probably unsolvable, but if you solve it you may help save the planet :P
TODO: text editor, tetris, voice synth?, snake, quadratic equation, fractals, 2D raycasting, fourier transform, primes, image library, web browser, diff, MD parser, solver/generator, markov chain, syntax beautifier, grep, some kinda server, function plotter, pi digits, 2D physics engine, encryption?, procedural MIDI, machine translation?, maze gen., genetic prog., language recognizer, AI?, photogrammetry, chat ...
TODO: text editor, tetris, voice synth?, snake, quadratic equation, fractals, 2D raycasting, fourier transform, primes, image library, web browser, diff, HTML parser/visualizer?, markov chain, syntax beautifier, grep, some kinda server, function plotter, pi digits, 2D physics engine, encryption?, custom markup lang, procedural MIDI, machine translation?, maze gen., genetic prog., language recognizer, AI?, photogrammetry, solar system simulator, emulator, chat (P2P?), auto integrator, steganography, driver? ...
## Quiz/Questions/Problems
## Quiz/Questions/Problems/Test
Here are some questions to test your LRS related knowledge :D
@ -103,12 +109,17 @@ Here are some questions to test your LRS related knowledge :D
12. Manually convert the [binary](binary.md) numeral 10110000000010110101 to hexadecimal.
13. How would you compute the circumference of a circle with radius *r* without using floating point? Consider just the approximate value of pi ~= 3.14, i.e. write the formula multiplying *2 * r* by 3.14 only using whole numbers (of course the result will be rounded to whole number too).
14. Name at least five licenses commonly used for [FOSS](foss.md) programs, five text editors/IDEs commonly used for programming and five operating systems whose source code is mostly free-licensed (none of these is allowed to be using the same or forked kernel of any other).
15. What is the minimum number of [bits](bit.md) that will allow us to represent 12345678910111213 distinct values?
15. What is the minimum number of [bits](bit.md) that will allow us to represent 12345678910111213 distinct values?
16. Give at least one example of [analog](analog.md) electronic device and one of [digital](digital.md) mechanical device.
17. Answer yes/no to following: Is base-three number 2101 greater than base-seven number 206? Is [gemini](gemini.md) better than [gopher](gopher.md)? Is there any [triangle](triangle.md) (in Euclidean geometry) whose one side is longer than the sum of lengths of its other two sides?
18. There are two walls 2 meters apart, the right wall is moving left by the speed 0.1 m/s, the left wall is moving right by the same speed 0.1 m/s. There is a fly in the middle between the walls, flying by speed 1 m/s. It is flying towards one wall, then when it reaches it it turns around and flies towards the other wall etc. When the walls completely close in, what distance would the fly have traveled? (There is a simple solution.)
20. In 3D computer [graphics](graphics.md) what's the difference between [shading](shading.md) and drawing [shadows](shadow.md)?
21. Can we say [neural networks](neural_network.md) are [Turing complete](turing_complete.md)? Explain why or why not.
22. 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?
### Answers
@ -132,6 +143,11 @@ Here are some questions to test your LRS related knowledge :D
18. The walls will collide in 10 seconds during which the fly has been constantly flying with the speed 1 m/s, so it traveled 10 meters.
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.
