63 lines
2.7 KiB
Markdown
63 lines
2.7 KiB
Markdown
# Sieve
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Write a program that uses the Sieve of Eratosthenes to find all the primes from 2 up to a given 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,
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starting with the multiples of 2.
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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.
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## Getting Started
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Make sure you have read the [getting started with C++](http://help.exercism.io/getting-started-with-cpp.html)
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page on the [exercism help site](http://help.exercism.io/). This covers
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the basic information on setting up the development environment expected
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by the exercises.
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## Passing the Tests
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Get the first test compiling, linking and passing by following the [three
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rules of test-driven development](http://butunclebob.com/ArticleS.UncleBob.TheThreeRulesOfTdd).
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Create just enough structure by declaring namespaces, functions, classes,
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etc., to satisfy any compiler errors and get the test to fail. Then write
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just enough code to get the test to pass. Once you've done that,
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uncomment the next test by moving the following line past the next test.
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```C++
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#if defined(EXERCISM_RUN_ALL_TESTS)
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```
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This may result in compile errors as new constructs may be invoked that
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you haven't yet declared or defined. Again, fix the compile errors minimally
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to get a failing test, then change the code minimally to pass the test,
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refactor your implementation for readability and expressiveness and then
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go on to the next test.
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Try to use standard C++11 facilities in preference to writing your own
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low-level algorithms or facilities by hand. [CppReference](http://en.cppreference.com/)
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is a wiki reference to the C++ language and standard library. If you
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are new to C++, but have programmed in C, beware of
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[C traps and pitfalls](http://www.slideshare.net/LegalizeAdulthood/c-traps-and-pitfalls-for-c-programmers).
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## Source
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Sieve of Eratosthenes at Wikipedia [view source](http://en.wikipedia.org/wiki/Sieve_of_Eratosthenes)
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