Programming Challenges @programming.dev Ategon @programming.dev 1y ago

[Easy] String Compression

Given a string, compress substrings of repeated characters in to a format similar to aaa -> a3

For example for the string aaabbhhhh33aaa the expected output would be a3b2h432a3

You must accept the input as a command line argument (entered when your app is ran) and print out the result

(It will be called like node main.js aaaaa or however else to run apps in your language)

You can use the solution tester in this post to test you followed the correct format https://programming.dev/post/1805174

Any programming language may be used. 1 point will be given if you pass all the test cases with 1 bonus point going to whoevers performs the quickest and 1 for whoever can get the least amount of characters

To submit put the code and the language you used below

People who have completed the challenge:

@[email protected] - N/A - 84 chars (javascript)
@[email protected] - 0.011s - 385 chars (python)
@[email protected]
- 0.003s - 487 chars (c) (fastest)
- 0.01s - 60 chars (javascript) (shortest)
@[email protected] - 0.005s - 530 chars (rust)
@[email protected] - 0.191s - 566 chars (python)
@[email protected] - 0.053s - 359 chars (factor) If you submitted in factor, ruby, cobol, etc. itll take me a bit longer to check since I havent set up running those yet. Should be soon

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My solution (runs in O(n) time, but so do all the other solutions so far as far as I can tell):

from itertools import pairwise

def main(s: str) -> str:
    characters = [None] + list(s) + [None]
    transitions = []
    for (_, left), (right_idx, right) in pairwise(enumerate(characters)):
        if left != right:
            transitions.append((right_idx, right))
    repeats = [(stop - start, char) for (start, char), (stop, _) in pairwise(transitions)]
    return ''.join(f'{char}{length}' for length, char in repeats)

if __name__ == '__main__':
    from argparse import ArgumentParser
    parser = ArgumentParser()
    parser.add_argument('s')
    print(main(parser.parse_args().s))

Runthrough:
'aaabb' -> [None, 'a', 'a', 'a', 'b', 'b', None] -> [(1, 'a'), (4, 'b'), (6, None)] -> [(4 - 1, 'a'), (6 - 4, 'b')]

Golfed (just for fun, not a submission):

import sys
from itertools import pairwise as p
print(''.join(c+str(b-a)for(a,c),(b,_)in p([(i,r)for i,(l,r)in enumerate(p([None,*sys.argv[1],None]))if l!=r])))

8/8 test cases passed

time taken: 0.191s

characters: 566

14 comments