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A tag is a keyword or label that categorizes your question with other, similar questions. Using the right tags makes it easier for others to find and answer your question.

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For challenges which consist of two adversary (and asymmetric) sub-challenges.
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For challenges regarding counting the number of occurrences of some characteristic.
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For challenges focusing on the optimization of an aspect not covered by other tags.
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Problems in geometry or graph theory that involve finding an optimal (e.g. shortest) path, subject to constraints (obstacles).
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related to the Python language. Note that challenges that require the answers to be in a specific language are generally discouraged.
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Tasks involving writing interpreters for various languages or formalisms.
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Problems involving processing of natural languages in a human way. Tasks include interpreting free text, correcting spelling or grammar, understanding pronunciation, etc.
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The challenge involves Fibonacci numbers or one of their generalizations.
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a strategic game played with two players on a checkered grid. This tag is for challenges related to chess or any variation on chess.
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For challenges involving code that runs in multiple programming languages.
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Code challenges that involve the use of regular expressions.
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Challenges pertaining to a sequence within a larger sequence
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if your challenge is about writing programs that solve puzzles such as Sudoku, Rubik's Cube, Crossword puzzles, etc.
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words, phrases, representations of numbers or times which read the same in reverse, for example "level", "reviver", "12321", "10:01". See also the [balanced-string] tag.
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indicates that the challenge requires answers to use the Internet to retrieve information.
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In a balanced string certain pairs of characters or substrings always appear with the same amount. Often there are additional restrictions that those pairs also have to be ordered. The most common exa…
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related to the JavaScript language. Note that challenges that require the answers to be in a specific language are generally discouraged.
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Related to compressing or decompressing arbitrary data. Challenges which relate to compressing a single specific input should instead be tagged [kolmogorov-complexity]
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indicates that the challenge involves converting from one format to another.
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The solution can only contain the 95 printable ASCII characters (space to ~). Tabs and newlines may be allowed as well, depending on the challenge.
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A challenge that involves making a "Hello, World!" program, or other similar strings.
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related to the BF language. Note that challenges that require the answers to be in a specific language are generally discouraged.
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for challenges involving board games.
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expected to generate code.
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For challenges involving the usage and manipulation of the alphabet.
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This challenge involves the manipulation of rational numbers, i.e. those which can be represented as a fraction of integers. Do not use this tag if rational numbers are just one of several admissible …
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indicates that the challenge involves music, e.g. taking music as input, producing music as output or handling musical notes.
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For challenges involving cryptography: encryption or decryption.
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code for these challenges will create some form of animated output
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scored by the number of operations in a specific fragment of a language you define.
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shapes that are self-similar and are usually quite detailed. Well-known fractal sets include the Mandelbrot set, Julia sets, and Phoenix sets. Tree-like fractal drawings are also common…
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For challenges which involve card games. This includes playing the game, implementing the game, as well as challenges concerned with individual mechanics and analysis of the game (for instance, comput…
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This challenge requires to label input data with a certain class, based on the properties of the data.
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Challenges which involve computing probabilities for random variables and stochastic processes.
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For challenges involving doing something on the bit level.
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For challenges involving unicode.