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123 lines
3.8 KiB
Markdown
123 lines
3.8 KiB
Markdown
# Crypto Square
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Implement the classic method for composing secret messages called a square code.
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Given an English text, output the encoded version of that text.
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First, the input is normalized: the spaces and punctuation are removed
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from the English text and the message is downcased.
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Then, the normalized characters are broken into rows. These rows can be
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regarded as forming a rectangle when printed with intervening newlines.
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For example, the sentence
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```text
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"If man was meant to stay on the ground, god would have given us roots."
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```
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is normalized to:
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```text
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"ifmanwasmeanttostayonthegroundgodwouldhavegivenusroots"
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```
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The plaintext should be organized in to a rectangle. The size of the
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rectangle (`r x c`) should be decided by the length of the message,
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such that `c >= r` and `c - r <= 1`, where `c` is the number of columns
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and `r` is the number of rows.
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Our normalized text is 54 characters long, dictating a rectangle with
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`c = 8` and `r = 7`:
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```text
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"ifmanwas"
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"meanttos"
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"tayonthe"
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"groundgo"
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"dwouldha"
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"vegivenu"
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"sroots "
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```
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The coded message is obtained by reading down the columns going left to
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right.
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The message above is coded as:
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```text
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"imtgdvsfearwermayoogoanouuiontnnlvtwttddesaohghnsseoau"
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```
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Output the encoded text in chunks that fill perfect rectangles `(r X c)`,
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with `c` chunks of `r` length, separated by spaces. For phrases that are
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`n` characters short of the perfect rectangle, pad each of the last `n`
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chunks with a single trailing space.
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```text
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"imtgdvs fearwer mayoogo anouuio ntnnlvt wttddes aohghn sseoau "
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```
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Notice that were we to stack these, we could visually decode the
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ciphertext back in to the original message:
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```text
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"imtgdvs"
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"fearwer"
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"mayoogo"
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"anouuio"
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"ntnnlvt"
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"wttddes"
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"aohghn "
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"sseoau "
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```
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## Exception messages
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Sometimes it is necessary to raise an exception. When you do this, you should include a meaningful error message to
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indicate what the source of the error is. This makes your code more readable and helps significantly with debugging. Not
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every exercise will require you to raise an exception, but for those that do, the tests will only pass if you include
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a message.
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To raise a message with an exception, just write it as an argument to the exception type. For example, instead of
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`raise Exception`, you should write:
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```python
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raise Exception("Meaningful message indicating the source of the error")
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```
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## Running the tests
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To run the tests, run the appropriate command below ([why they are different](https://github.com/pytest-dev/pytest/issues/1629#issue-161422224)):
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- Python 2.7: `py.test crypto_square_test.py`
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- Python 3.4+: `pytest crypto_square_test.py`
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Alternatively, you can tell Python to run the pytest module (allowing the same command to be used regardless of Python version):
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`python -m pytest crypto_square_test.py`
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### Common `pytest` options
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- `-v` : enable verbose output
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- `-x` : stop running tests on first failure
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- `--ff` : run failures from previous test before running other test cases
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For other options, see `python -m pytest -h`
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## Submitting Exercises
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Note that, when trying to submit an exercise, make sure the solution is in the `$EXERCISM_WORKSPACE/python/crypto-square` directory.
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You can find your Exercism workspace by running `exercism debug` and looking for the line that starts with `Workspace`.
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For more detailed information about running tests, code style and linting,
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please see [Running the Tests](http://exercism.io/tracks/python/tests).
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## Source
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J Dalbey's Programming Practice problems [http://users.csc.calpoly.edu/~jdalbey/103/Projects/ProgrammingPractice.html](http://users.csc.calpoly.edu/~jdalbey/103/Projects/ProgrammingPractice.html)
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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 have completed the exercise.
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