This notebook was prepared by [Donne Martin](http://donnemartin.com). Source and license info is on [GitHub](https://github.com/donnemartin/interactive-coding-challenges).

Challenge Notebook

Problem: Compress a string such that 'AAABCCDDDD' becomes 'A3B1C2D4'. Only compress the string if it saves space.

Constraints
Test Cases
Algorithm
Code
Unit Test
Solution Notebook

Constraints

Can we assume the string is ASCII?
- Yes
- Note: Unicode strings could require special handling depending on your language
Can you use additional data structures?
- Yes
Is this case sensitive?
- Yes

Test Cases

None -> None
'' -> ''
'AABBCC' -> 'AABBCC'
'AAABCCDDDD' -> 'A3B1C2D4'

Algorithm

Refer to the Solution Notebook. If you are stuck and need a hint, the solution notebook's algorithm discussion might be a good place to start.

Code



In [ ]:

    
def compress_string(string):
    # TODO: Implement me
    pass

Unit Test

The following unit test is expected to fail until you solve the challenge.



In [ ]:

    
# %load test_compress.py
from nose.tools import assert_equal


class TestCompress(object):

    def test_compress(self, func):
        assert_equal(func(None), None)
        assert_equal(func(''), '')
        assert_equal(func('AABBCC'), 'AABBCC')
        assert_equal(func('AAABCCDDDD'), 'A3B1C2D4')
        print('Success: test_compress')


def main():
    test = TestCompress()
    test.test_compress(compress_string)


if __name__ == '__main__':
    main()

Solution Notebook

Review the Solution Notebook for a discussion on algorithms and code solutions.