Update

exercises.md

@@ -32,17 +32,20 @@ Here you will find suggestions for programming projects, roughly sorted by their
 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.
 
 ### Level 1: Easy, *I'm Too Young To Die*
 
 1. **[fizzbuzz](fizzbuzz.md)**: Write the classic fizzbuzz program.
 2. **[anagram](anagram.md) checker**: Make a program that reads one line of text from the user and checks if it's an anagram (i.e. if it's spelled the same forward and backwards) or not -- you can just output *yes* or *no*.
 3. **number [encyclopedia](encyclopedia.md)**: Make a program that writes numbers from 0 to 1000 (including both) and about each of which it writes some facts. These facts have to include at least the number's square, square root, sum of its decimal digits, its [binary](binary.md) representation, prime factorization and whether the number itself is [prime](prime.md), perfect number and [Fibonacci](fibonnaci.md) number.
-4. **[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.
-5. **[game of life](game_of_life.md)**: Make a program that simulates game of life on a finite *N * N* grid, with wrapping space (i.e. a cell on the very left of the grid is considered a neighbor of the cell on the very right in the same row, same thing with top and bottom). Make *N* configurable at least as a compile time option, draw the world as [ASCII art](ascii_art.md) to terminal, make the user step forward by pressing some key. You can initialize the grid values randomly, but thumbs up for allowing setting the initial world state (e.g. reading it from a file or something).
-6. **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.
-7. **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.
-8. **[bytebeat](bytebeat.md)**: Make at least three cool sounding bytebeat songs.
+4. **[game of life](game_of_life.md)**: Make a program that simulates game of life on a finite *N * N* grid, with wrapping space (i.e. a cell on the very left of the grid is considered a neighbor of the cell on the very right in the same row, same thing with top and bottom). Make *N* configurable at least as a compile time option, draw the world as [ASCII art](ascii_art.md) to terminal, make the user step forward by pressing some key. You can initialize the grid values randomly, but thumbs up for allowing setting the initial world state (e.g. reading it from a file or something).
+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.
+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.
 
 ### Level 2: Mid, *Hurt Me Plenty*
 
@@ -56,6 +59,7 @@ Here you will find suggestions for programming projects, roughly sorted by their
 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. **[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.
+11. **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*
 
@@ -69,6 +73,7 @@ Here you will find suggestions for programming projects, roughly sorted by their
 8. **64K intro**: Make an impressive [demoscene](demoscene.md)-style 3D intro with music. It must have duration of at least 1 minute and fit into a 64 KB executable. It has to be good enough so that an average demoscener would approve it as not completely laughable.
 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).
 
 ### Level 4: God Tier, *!Nightmare!*
 
@@ -78,7 +83,7 @@ Here you will find suggestions for programming projects, roughly sorted by their
 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
 
-TODO: text editor, tetris, voice synth?, snake, JPG like compression, quadratic equation, fractals, 2D raycasting, fourier transform, primes, image library, web browser, diff, MD parser, solver/generator, bytebeat, markov chain, syntax beautifier, grep, some kinda server, function plotter, raytracer, pi digits, 2D physics engine, encryption?, procedural MIDI, machine translation?, maze gen., genetic prog., language recognizer, search engine, AI?, chat ...
+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 ...
 
 ## Quiz/Questions/Problems
 
@@ -97,12 +102,19 @@ Here are some questions to test your LRS related knowledge :D
 11. What's the worst socioeconomic system in the world? You don't even have to say why because that would take too long.
 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?
+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.)
+19. Solve these [anagrams](anagram.md): *no cure sir*, *come piss ron*, *ginger*, *nicer shops*, *fog tag*, *trek now*.
+20. In 3D computer [graphics](graphics.md) what's the difference between [shading](shading.md) and drawing [shadows](shadow.md)?
 
 ### Answers
 
 1. Though legally similar (but not identical), free software is a movement based on ethics and pursuing freedom for the software user, open source is evil business movement that avoids talking about ethics, it was forked from free software and is solely focused on exploiting free software licenses for making profit.
 2. [C](c.md), [C++](cpp.md), [Java](java.md), [JavaScrip](javascript.md), [Python](python.md), [Lisp](lisp.md), [Forth](forth.md), [Brainfuck](brainfuck.md), [Fortran](fortran.md), [Pascal](pascal.md), [Haskell](haskell.md), [Prolog](prolog.md), [Smalltalk](smalltalk.md), [comun](comun.md), ...
-3. The mirror doesn't flip the text, you flipped it by pointing it at the mirror -- you most likely flipped it horizontally so that's how you see it in the mirror, but you could as well have flipped it vertically; then the text would be flipped vertically in the mirror.
+3. The mirror doesn't really flip the text -- what's left/right in front of it is also left/right in it. It is you who flipped the text when you pointed it at the mirror -- you most likely flipped it horizontally so that's how you see it in the mirror, but you could as well have flipped it vertically; then the text would be flipped vertically in the mirror.
 4. Modulo bias happens when the random number generator's range is non-divisible by our desired range that we enforce with modulo operator -- with shown approach some numbers then have higher probability of being generated than others. For example if rand() here return numbers from 0 to 1023, there is only one way to get 999 (999 % 1000) but two ways to get 0 (0 % 1000 and 1000 % 1000), i.e. 0 is more likely to be generated. Common approach to reducing this effect is to repeatedly generate numbers until we get one falling into the "fair" range (this is not guaranteed to end so we should limit the maximum number of attempts).
 5. The relationship is commonly described like this: information is interpreted data. I.e. data is just a sequence of symbols, information is the knowledge we extract from it.
 6. The probability of program breaking is 1 minus probability of it not breaking. For a program to NOT break during one year, all libraries have to stay unchanged (probability 0.95 for each one): that's 0.95 * 0.95 * 0.95 * ... = 0.95^10. Similarly the probability of it not breaking during 5 years is (0.95^10)^5, so the probability of the program breaking in 5 years is around 92%.
@@ -112,4 +124,15 @@ Here are some questions to test your LRS related knowledge :D
 10. two (try it, see coin rotation paradox)
 11. [capitalism](capitalism.md)
 12. B00B5
-13. *(2 * r * 314) / 100*
+13. *(2 * r * 314) / 100*
+14. [GPL](gpl.md), LGPL, AGPL, [MIT](mit.md), BSD, Apache, [CC0](cc0.md), unlicense, zlib, WTFPL, ...; [vim](vim.md), [emacs](emacs.md), [Acme](acme.md), Geany, vi, Notepad++, Neovim, Kate, nano, gedit, ...; [Debian](debian.md), 9front, [OpenBSD](openbsd.md), [FreeDOS](freedos.md), [Haiku](haiku.md), [Minix](minix.md), ReactOS, [GNU](gnu.md)/[Hurd](hurd.md), V6 [Unix](unix.md), FreeRTOS, ...
+15. The number is *N* such that 2^N = 12345678910111213, rounded up, that is ceil(log2(12345678910111213)) = 54.
+16. amplifier, voltmeter, analog hardware for [neural networks](neural_net.md), ...; abacus, mechanical calculators such as Curta, Turing machine made of wood, ...
+17. no, no, no
+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.
+19. *[recursion](recursion.md)*, *[compression](compression.md)*, *[nigger](nigger.md)*, *[censorship](censorship.md)*, *[faggot](faggot.md)*, *[network](network.md)*.
+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.
+
+## 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.