regex oneliner clear solution for Double Substring by StefanPochmann - python coding challenges

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regex oneliner solution in Clear category for Double Substring by StefanPochmann

import re

def double_substring(line):
    return max(map(len, re.findall(r'(?=(.*).*\1)', line)))

Aug. 14, 2017

Comments:

J.W on March 19, 2018, 5:29 p.m.
smart

StupidYe on Sept. 14, 2018, 4:01 a.m.
the code is well!

StupidYe on Sept. 14, 2018, 6:12 a.m.
Can you explain what it is means? <pre class='brush: python'>?=(.*).*\1 </pre>

Oksana_Antropova on March 31, 2019, 4:32 a.m.
Actually, it's (?=(.).\1). Dont's forget the external brackets. . - any symbol except '\n' * - 0 or more repetitions of the previous symbol .* - several symbols (.*) - brackets are a capturing group. It is used to catch and "memorize" what we matched inside the brackets (a repeating substring we are looking for) next .* means that there might be any number (including 0) of symbols between the repetitions \1 means the same string we found in the first capturing group (our substring). (?=pattern) - is a positive lookahead. It matches if pattern matches next, but doesn’t consume any of the string. In terms of our task it helps us to find all the repeating substrings. If we typed just '(.*).*\1' (without the lookaround), we would find only the first repeating substring, because it would consume some parts of the string and wouldn't be able to find the other repeating substrings.

nameless666 on Dec. 28, 2019, 4:16 p.m.
thank you

Kolia951 on July 11, 2023, 12:06 p.m.
I would add that the positive lookahead assertion is necessary here only because a regex expression finds only nonoverlapping substrings, while a group inside the positive lookahead assertion will find all possible groups mathes with an expression `(.).\1`

Kolia951 on July 11, 2023, 12:07 p.m.
I would add that the positive lookahead assertion is necessary here only because a regex expression finds only nonoverlapping substrings, while a group inside the positive lookahead assertion will find all possible groups mathes with an expression (.).\1

Bowie_Wang on April 24, 2019, 3:22 p.m.
your code is amazing.

Frazer-dl on Oct. 4, 2019, 8:08 a.m.
What does mean "len" in map function?

Strings Theory

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