65 lines
2.3 KiB
Markdown
65 lines
2.3 KiB
Markdown
# Prime Factors
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Compute the prime factors of a given natural number.
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A prime number is only evenly divisible by itself and 1.
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Note that 1 is not a prime number.
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## Example
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What are the prime factors of 60?
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- Our first divisor is 2. 2 goes into 60, leaving 30.
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- 2 goes into 30, leaving 15.
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- 2 doesn't go cleanly into 15. So let's move on to our next divisor, 3.
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- 3 goes cleanly into 15, leaving 5.
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- 3 does not go cleanly into 5. The next possible factor is 4.
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- 4 does not go cleanly into 5. The next possible factor is 5.
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- 5 does go cleanly into 5.
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- We're left only with 1, so now, we're done.
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Our successful divisors in that computation represent the list of prime
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factors of 60: 2, 2, 3, and 5.
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You can check this yourself:
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- 2 * 2 * 3 * 5
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- = 4 * 15
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- = 60
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- Success!
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## Getting Started
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Make sure you have read [the C++ page](http://exercism.io/languages/cpp) on
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exercism.io. This covers the basic information on setting up the development
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environment expected 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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The Prime Factors Kata by Uncle Bob [view source](http://butunclebob.com/ArticleS.UncleBob.ThePrimeFactorsKata)
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