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74 lines
2.8 KiB
Markdown
74 lines
2.8 KiB
Markdown
# Run Length Encoding
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Implement run-length encoding and decoding.
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Run-length encoding (RLE) is a simple form of data compression, where runs
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(consecutive data elements) are replaced by just one data value and count.
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For example we can represent the original 53 characters with only 13.
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```text
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"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB" -> "12WB12W3B24WB"
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```
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RLE allows the original data to be perfectly reconstructed from
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the compressed data, which makes it a lossless data compression.
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```text
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"AABCCCDEEEE" -> "2AB3CD4E" -> "AABCCCDEEEE"
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```
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For simplicity, you can assume that the unencoded string will only contain
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the letters A through Z (either lower or upper case) and whitespace. This way
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data to be encoded will never contain any numbers and numbers inside data to
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be decoded always represent the count for the following character.
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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 run_length_encoding_test.py`
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- Python 3.4+: `pytest run_length_encoding_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 run_length_encoding_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/run-length-encoding` 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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Wikipedia [https://en.wikipedia.org/wiki/Run-length_encoding](https://en.wikipedia.org/wiki/Run-length_encoding)
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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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