77 lines
2.8 KiB
Markdown
77 lines
2.8 KiB
Markdown
# Sieve
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Use the Sieve of Eratosthenes to find all the primes from 2 up to a given
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number.
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The Sieve of Eratosthenes is a simple, ancient algorithm for finding all
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prime numbers up to any given limit. It does so by iteratively marking as
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composite (i.e. not prime) the multiples of each prime, starting with the
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multiples of 2. It does not use any division or remainder operation.
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Create your range, starting at two and continuing up to and including the given limit. (i.e. [2, limit])
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The algorithm consists of repeating the following over and over:
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- take the next available unmarked number in your list (it is prime)
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- mark all the multiples of that number (they are not prime)
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Repeat until you have processed each number in your range.
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When the algorithm terminates, all the numbers in the list that have not
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been marked are prime.
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The wikipedia article has a useful graphic that explains the algorithm:
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https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes
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Notice that this is a very specific algorithm, and the tests don't check
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that you've implemented the algorithm, only that you've come up with the
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correct list of primes. A good first test is to check that you do not use
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division or remainder operations (div, /, mod or % depending on the
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language).
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Run the tests with:
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```bash
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bats sieve_test.sh
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```
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After the first test(s) pass, continue by commenting out or removing the
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`[[ $BATS_RUN_SKIPPED == true ]] || skip`
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annotations prepending other tests.
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To run all tests, including the ones with `skip` annotations, run:
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```bash
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BATS_RUN_SKIPPED=true bats sieve_test.sh
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```
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## Source
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Sieve of Eratosthenes at Wikipedia [http://en.wikipedia.org/wiki/Sieve_of_Eratosthenes](http://en.wikipedia.org/wiki/Sieve_of_Eratosthenes)
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## External utilities
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`Bash` is a language to write "scripts" -- programs that can call
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external tools, such as
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[`sed`](https://www.gnu.org/software/sed/),
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[`awk`](https://www.gnu.org/software/gawk/),
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[`date`](https://www.gnu.org/software/coreutils/manual/html_node/date-invocation.html)
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and even programs written in other programming languages,
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like [`Python`](https://www.python.org/).
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This track does not restrict the usage of these utilities, and as long
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as your solution is portable between systems and does not require
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installation of third party applications, feel free to use them to solve
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the exercise.
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For an extra challenge, if you would like to have a better understanding
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of the language, try to re-implement the solution in pure `Bash`,
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without using any external tools. Note that there are some types of
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problems that bash cannot solve, such as performing floating point
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arithmetic and manipulating dates: for those, you must call out to an
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external tool.
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## Submitting Incomplete Solutions
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It's possible to submit an incomplete solution so you can see how others
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have completed the exercise.
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