64 lines
2.2 KiB
Markdown
64 lines
2.2 KiB
Markdown
# Difference Of Squares
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Find the difference between the square of the sum and the sum of the squares of the first N natural numbers.
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The square of the sum of the first ten natural numbers is
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(1 + 2 + ... + 10)² = 55² = 3025.
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The sum of the squares of the first ten natural numbers is
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1² + 2² + ... + 10² = 385.
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Hence the difference between the square of the sum of the first
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ten natural numbers and the sum of the squares of the first ten
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natural numbers is 3025 - 385 = 2640.
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You are not expected to discover an efficient solution to this yourself from
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first principles; research is allowed, indeed, encouraged. Finding the best
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algorithm for the problem is a key skill in software engineering.
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Run the tests with:
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```bash
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bats difference_of_squares_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 difference_of_squares_test.sh
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```
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## Source
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Problem 6 at Project Euler [http://projecteuler.net/problem=6](http://projecteuler.net/problem=6)
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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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